Preheat oven to 350°F (175°C) and line a mini muffin tray.
Mash bananas in a bowl.
In another bowl, mix flour, baking powder, baking soda, and salt.
In a separate bowl, whisk sugar, egg, oil, and vanilla.
Fold in dry ingredients and mashed bananas.
Spoon batter into the tray, filling each ⅔ full.
Bake for 12-15 minutes or until a toothpick comes out clean.
Let cool for 5 minutes before transferring to a wire rack.