Preheat oven to 350 degrees F (175 degrees C). Coat muffin pans with non-stick spray. Sift together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt; set aside.
In a mixer add the bananas- turn speed to 2 and allow the mixer to smash them. Add the sugar, egg, and melted butter in the bowl. Allow them to combine. Turn off the mixer and LIGHTLY fold in flour mixture, and mix until smooth. Please don't overmix. Scoop into the greased muffin pans.
Bake in the preheated oven. Bake mini muffins for 10 to 15 minutes, and large muffins for 25 to 30 minutes. Muffins will spring back when lightly tapped. Check the muffins 2 minutes before the end time to be sure not to over bake.