For nut-free option, substitute peanut butter with sunflower seed butter (note: sunflower seed butter may turn green after baking, which is safe)., To add crunch, incorporate chopped walnuts, pecans, or coconut flakes into the batter., For more chocolate flavor, add a spoonful of chocolate hazelnut spread in the center of each muffin before baking., Bananas can be replaced with 3/4 cup unsweetened applesauce or pumpkin puree, which will slightly alter the flavor but maintain moisture., Use muffin liners to prevent sticking due to the moist batter; if unavailable, grease muffin tins thoroughly with butter and cooking spray., Store muffins at room temperature in an airtight container lined with paper towels for 1-3 days; refrigerate for up to one week or freeze wrapped individually for up to 3 months., Mix batter the night before and refrigerate; stir gently before baking the next day., For gluten-free version, swap all-purpose flour with gluten-free flour blend and verify protein powder is gluten-free., For dairy-free, use dairy-free yogurt, milk alternatives, and dairy-free protein powder., Avoid overmixing and overbaking to keep muffins moist and tender.