Squeeze moisture out of zucchini to prevent soggy muffins., Use pure pumpkin puree only; avoid pumpkin pie filling which contains added sugars and spices., Gently mix batter after adding dry ingredients to avoid tough muffins; some lumps are okay., Fill muffin cups about two-thirds full for proper rising without overflow., Use muffin liners or grease pan wells well to prevent sticking and for easy removal., Topping can be made flakier by using cold butter or chilling before applying., For nut allergies, substitute walnuts with pumpkin or sunflower seeds or omit nuts entirely., Muffins can be stored airtight at room temperature up to 3 days or frozen up to 3 months., Reheat refrigerated or frozen muffins in microwave (15-30 seconds) or oven (8-10 minutes at 300°F) to refresh., Optional mix-ins include chocolate chips, dried cranberries or raisins, vanilla extract., No streusel topping options include plain muffins, cinnamon cream cheese frosting, or powdered sugar dusting.