Spinach Mushroom Breakfast Casserole

This Spinach Mushroom Breakfast Casserole is an easy vegetarian egg bake loaded with spinach, mushrooms, and creamy goat cheese. Perfect for breakfast or brunch, it’s always a hit with family and friends!

One of the reasons I adore breakfast casseroles is how easy they are to pull together. Think of it as a giant frittata packed with eggs and whatever veggies, cheese, and meats you love. This Spinach Mushroom Breakfast Casserole is one of my absolute favorites! It’s hearty, full of flavor, and totally satisfying. Plus, it’s vegetarian, so it fits a lot of diets and tastes great at the start of any day.

Since this casserole makes a big batch, it’s ideal for feeding a crowd—like holiday mornings or brunch gatherings with friends. But if it’s just your family, no worries! The leftovers are fantastic reheated and make mornings so much easier when you’re rushing around. Trust me, having this ready to go in the fridge is a total lifesaver!

If you’re after a simple, crowd-pleasing breakfast or brunch that’s vegetarian, packed with nutrients, and just bursting with flavor, this Spinach Mushroom Breakfast Casserole is definitely for you. Earthy cremini mushrooms, vibrant fresh spinach, and creamy goat cheese fold seamlessly into a big batch of eggs, all baked in a 9×13-inch dish that serves up to 12 hungry people.

This dish couldn’t be easier to make. You’ll soften the veggies on the stove, whisk eggs with a splash of milk, then combine it all in a greased pan to bake until perfectly set. It takes about 30 to 45 minutes depending on your oven, and it reheats like a dream or freezes beautifully for later.

• Feeds roughly 12—perfect for gatherings or prepping ahead.
• Make-ahead friendly and freezes well for stress-free breakfasts.
• Super flexible—try swapping cheeses, tossing in cooked meat, or adjusting veggies to your liking.

Why You’ll Love It

This casserole hits all the right notes for a comforting, easy, and flavorful meal. Here’s why it’s become a go-to in our house:

• Feeds a crowd: With about 12 servings, it’s wonderful for holiday brunches, potlucks, or big family breakfasts that bring everyone to the table. For a sweet-and-savory spread, pair it with a Puff Pastry Breakfast Tart.
• Make-ahead and freezer-friendly: You can assemble it the night before or freeze portions for quick mornings when time is tight.
• Vegetarian and veggie-packed: It’s loaded with spinach and mushrooms, which add nutrients, texture, and make it super filling, even without meat.
• Protein boost: Packed with eggs, each serving has around 12 grams of protein to keep you fueled and satisfied.
• Bold, simple flavors: The earthy mushrooms, fresh green onions, and tangy goat cheese come together easily but taste like you spent hours cooking. If you love mushroom-forward bites, try these Mushroom Puff Pastry Appetizers.
• Flexible and forgiving: Don’t love goat cheese? Swap in feta, mozzarella, or whatever cheese you have. Want meat? Add bacon or sausage. Want more veggies? Go for it!
• Great leftovers: Keeps well in the fridge for up to 4 days and reheats wonderfully, making breakfasts simple all week long.

Seriously, between how easy it is, the nutrition, and the crowd-pleasing factor, this Spinach Mushroom Breakfast Casserole will quickly become one of your favorite breakfast staples.

This casserole is a dream for mornings when you need something filling, flavorful, and hands-off. Whether it’s a busy weekday or a relaxed holiday brunch, this dish fits perfectly. Earthy mushrooms, bright spinach, and tangy goat cheese get baked into a big batch of eggs that not only tastes incredible but also makes mornings manageable with leftovers that reheat beautifully.

• Great for feeding about 12 people—ideal for big groups or making ahead.
• Freezer and make-ahead friendly so you can have quick breakfasts anytime.
• Easy to customize with different cheeses, meats, or veggies based on what you like and what’s in your fridge.
• Combines good servings of veggies with plenty of protein for a balanced meal.

What You’ll Need

• 1 tablespoon olive oil
• 16 ounces cremini mushrooms, sliced
• 4 cups packed spinach leaves
• 3 cloves garlic, minced
• Kosher salt and black pepper, to taste
• 2 green onions, sliced
• 4 ounces goat cheese, divided
• 18 large eggs
• 1/2 cup milk
• Freshly chopped chives for garnish, optional

How to Make It

1. Preheat oven to 350°F and grease a 9×13-inch baking dish with nonstick spray or butter.
2. Heat 1 tablespoon olive oil in a large skillet over medium-high heat.
3. Add 16 ounces sliced cremini mushrooms and cook until softened and beginning to brown, about 3 minutes.

4. Add 4 cups packed fresh spinach and 3 minced garlic cloves; cook, stirring, until spinach wilts, about 2–3 minutes; season with kosher salt and black pepper and remove from heat.

   
5. Transfer the cooked mushrooms and spinach to the prepared baking dish and spread into an even layer.
6. Scatter 2 sliced green onions over the vegetables and crumble half of the 4 ounces of goat cheese on top.
7. In a large bowl, whisk 18 large eggs and 1/2 cup milk until smooth; season with salt and pepper.

8. Pour the egg mixture evenly over the vegetables and cheese in the baking dish.

   

9. Crumble the remaining goat cheese over the top of the eggs.
10. Bake at 350°F, checking at 30 minutes, until the edges are golden and the center is set and no longer jiggly (about 30–50 minutes, typically ~45 minutes).
11. Remove the casserole from the oven and let rest about 5 minutes to firm up.

12. Garnish with freshly chopped chives if desired and cut into squares.

    

Pro Tips for Success

• When measuring spinach, pack it into the cup because it shrinks a lot when cooked. If you’re using frozen spinach, thaw it fully and squeeze out all the water so your casserole isn’t watery—see how to thoroughly drain frozen spinach.
• Cook mushrooms on fairly high heat until their moisture mostly evaporates, which prevents a soggy casserole.
• Make sure to grease your baking dish really well with nonstick spray or butter so the casserole slides out easily.
• Whisk eggs and milk thoroughly and season well to make sure every bite is flavorful.
• Check your casserole starting at 30 minutes. A golden edge and fully set center means it’s ready to come out.
• Letting it rest for 5 minutes before serving helps you get clean slices and lets the flavors settle.
• If freezing, cool completely, then wrap tightly in plastic wrap and foil or use a freezer-safe container. Thaw overnight in the fridge and bake at 350°F until piping hot.

Add-Ins and Substitutions

If you’re planning a big breakfast or brunch spread, here are a couple of our favorite sides that pair beautifully with this casserole—like a pan of Cracker Barrel Hashbrown Casserole and a batch of Homemade Cinnamon Rolls.

• Crispy bacon or savory sausage to add a meaty touch.
• Fresh fruit or fruit salad for a sweet and refreshing balance.

How to Store and Reheat

This spinach mushroom egg casserole keeps well in the fridge for up to four days. Once it’s cooled to room temp, cover your pan tightly with foil or plastic wrap, or transfer leftovers to an airtight container before refrigerating.

To reheat, pop the whole casserole in the oven at 350ºF for about 25 minutes, or microwave individual servings for 30 to 60 seconds—perfect for quick mornings (or try this easy Blueberry Cottage Cheese Breakfast Bake for another make-ahead option).

You can definitely freeze this breakfast casserole for up to two months. Just make sure it’s fully cooled before wrapping it tightly in plastic and foil or placing it in a freezer-safe container.

When you’re ready to eat, thaw it overnight in the fridge and then bake at 350ºF until warmed through, around 25 minutes. Freezing individual portions works great too—just defrost in the fridge and microwave for that easy breakfast on-the-go (these Sourdough Discard Breakfast Pockets are great for grab-and-go, too).

Common Questions Answered

• Q: Can I assemble this ahead of time?

  A: Absolutely! You can cook the veggies and put the casserole together the night before. Just cover it and refrigerate overnight, then bake it straight from the fridge the next morning. For another overnight-friendly breakfast bake, try our Eggnog French Toast Casserole. Baking might take a few extra minutes.

• Q: Can I use frozen spinach instead of fresh?

  A: Yes, you can. Just be sure to thaw it fully and squeeze out as much water as you can before tossing it in. For a quick visual on squeezing frozen spinach dry, see the steps in our Hot Spinach Dip. This keeps your casserole from getting watery.

• Q: Is this recipe gluten-free?

  A: Yes, all the ingredients listed are naturally gluten-free. If you’re adding processed items like sausage, just double-check their labels to make sure they don’t contain gluten.

• Q: Can I swap the goat cheese for another cheese?

  A: Definitely! Feta, shredded mozzarella, cheddar, fontina, or Parmesan all make great substitutes. Use whatever cheese you love or have on hand.

• Q: Can I add meat to this casserole?

  A: Yes, you can add cooked bacon, sausage, or ham. Just make sure it’s fully cooked before folding it into the casserole.

• Q: How long should I bake the casserole?

  A: Bake at 350°F for around 30–45 minutes. Ovens vary, so start checking at 30 minutes. It’s done when the edges are golden brown and the center feels firm (not jiggly).

• Q: How should I store leftovers?

  A: Keep leftovers covered in the fridge for up to four days. Reheat the whole pan in a 350°F oven for about 25 minutes, or microwave single servings for 30–60 seconds.

• Q: How many servings does this recipe make?

  A: This recipe serves about 12 people.