Preheat oven to 350℉. Coat muffin pans with non-stick spray, or use paper liners. Sift together the flour, baking powder, baking soda, and salt; set aside.
Combine bananas, sugar, egg, vanilla, cinnamon, and melted butter in a large bowl. Fold in flour mixture, and mix until smooth. Scoop into muffin pans using a 3-tablespoon scoop.
Bake in preheated oven. Bake muffins for 25 to 30 minutes. Muffins will spring back when lightly tapped.