Preheat oven to 350°F. Line a 12-cup muffin tin and 2 more wells* in a second tin with paper liners or lightly grease.
In a large bowl, whisk together bananas, pumpkin puree, both sugars, oil, eggs, and vanilla until smooth.
In a separate bowl, whisk together flour, baking soda, baking powder, pumpkin spice, and sea salt.
Add dry ingredients to wet ingredients and stir gently until just combined (don’t overmix). Fold in nuts or chocolate chips if using.
Divide batter evenly among muffin cups, filling about ¾ full.
Bake for 20–24 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.