Preheat oven to 375°F. Line a muffin pan with papers or coat with nonstick spray.
In a bowl, combine flour, oats, baking powder, baking soda, salt, and cinnamon.
In a large bowl or bowl of a stand mixer, cream together butter and brown sugar. Add bananas and mix, then mix in eggs.
Gradually add dry ingredients to banana mixture, mixing just until fully incorporated and no dry bits remain.
Divide batter among muffin cups. Bake for 18-20 minutes, until golden and a toothpick inserted in the center only has moist crumbs. Let cool in the pan a few minutes before removing to a wire rack to cool completely.