Preheat oven to 400° F. Fill muffin tin with paper liners.
Mash bananas and set aside.
In a medium mixing bowl, combine flour, oats, sugar, baking powder, baking soda, and salt.
In a large mixing bowl, lightly beat the egg, then stir in the milk, oil, and vanilla.
Add the mashed bananas to the wet ingredients and stir until combined.
Add the flour mixture and stir just until combined.
Fill each muffin cup 3/4 way full and bake for 18-20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Allow to cool in the pan for 5 minutes, then transfer to a wire rack to finish cooling.