Preheat the oven to 400°F, and line two muffin pans with 18 muffin liners.

In a medium bowl, mash the bananas. Then add the oats and milk. Set aside.

In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Set aside.

In a large bowl, use an electric mixer to beat together the butter and sugar until fluffy, about 3 minutes. Add the eggs and vanilla, and beat until combined.

Add half the oat mixture and half of the flour mixture, beating between additions. Continue until all the dry ingredients are added.

Fill each muffin liner ½ - ⅔ of the way full. Bake for 15 -18 minutes or until a toothpick inserted in the center comes out clean.