Preheat oven to 425° and line a 12-count muffin tray with liners.
In a large bowl, microwave butter until melted, about 15-20 seconds, then add the bananas and mash. Add the sugar and pumpkin. Stir well.
Stir in the egg and vanilla.
Add the pumpkin spice, cinnamon, flour, salt, and baking soda. Mix until no dry pockets remain.
Spoon evenly into the muffin tin.
Bake for 5 minutes at 425°, keeping the muffins in the oven, reduce the heat to 350° and bake for 15-16 more minutes. Baking them at the higher temperature at first helps them rise and gives a nice rounded top.