Preheat oven to 350°F (177°C). Line an 8 inch by 8 inch baking pan with parchment paper.
Add bananas to a large mixing bowl and use a fork or whisk to mash until the bananas are finely mashed.
Add the eggs to the mashed bananas and whisk until evenly combined and no egg streaks remain.
Add the oat flour and baking powder. Gently stir and fold with a spatula until they are fully incorporated and there are no pockets of oat flour in the batter. If adding any mix-ins, stir them in now. (For the photos, I added some bittersweet chocolate chips).
Pour the batter into the prepared pan and use a spatula to spread it evenly across. (I also sprinkled some additional bittersweet chocolate chips on top for decoration.)
Bake for 30-40 minutes or until the bars are done. The surface should be golden brown and puffed. When you apply light pressure to the surface, it should also bounce back a little and not completely sink in. The bars will initially be very puffy but they will sink down and level as they cool. Let bars cool completely before cutting with a sharp knife and serving. Keep any leftover uneaten bars stored in an airtight container in the fridge.
