Prep your pan. Heat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or grease well.
Mix the wet ingredients. In a large bowl, whisk together mashed bananas, pumpkin puree, eggs, oil, brown sugar, granulated sugar, and vanilla until smooth.
Whisk the dry ingredients. In a separate bowl, whisk flour, baking soda, baking powder, cinnamon, nutmeg, ginger, and salt until evenly combined.
Combine gently. Add dry ingredients to wet.
Stir with a spatula just until no dry streaks remain. Do not overmix. Fold in any add-ins.
Fill the cups. Divide batter evenly among the muffin cups, filling each about 3/4 full.
Bake. Bake 18–22 minutes, until the tops spring back when lightly pressed and a toothpick comes out with a few moist crumbs.
Cool. Let muffins cool in the pan for 5 minutes, then move to a wire rack. Enjoy warm or at room temp.