Preheat oven to 350°F (177°C). Line an 8 inch by 8 inch baking pan with parchment paper.
Add mashed bananas and eggs to a large mixing bowl. Whisk until there is no more egg streaks in the mixture and the mixture is mostly uniform (a few small chunks of bananas are okay). Add in oats and stir with a spatula until the oats are evenly mixed in. If adding any mix-ins, add them in now.
Transfer the batter to your prepared baking pan. Use a spatula to evenly spread it across the pan and smooth the surface.
Bake for about 20-30 minutes or until bars look set and cooked. The surface of the bars should be lightly golden and when you press lightly on the surface, it should feel lightly firm and bounce back rather than be very soft and sink in. Let bars cool fully before removing from the pan and cutting and serving. Store uneaten bars in an airtight container in the fridge or freezer.
