Prep the pan. Heat oven to 350°F (175°C).
Line an 8x8-inch or 9x9-inch square pan with parchment, leaving overhang for easy lifting.
Make oat flour if needed. Blend rolled oats in a blender until fine. Measure after blending to ensure 2 cups.
Mash the bananas. In a large bowl, mash bananas until mostly smooth with a few small lumps.
Whisk in wet ingredients. Add eggs, maple syrup, melted coconut oil, applesauce, and vanilla. Whisk until well combined.
Add dry ingredients. Sprinkle oat flour, baking soda, baking powder, salt, and cinnamon over the wet mixture.
Stir with a spatula until just combined. Do not overmix.
Fold in extras. If using chocolate chips, nuts, or fruit, fold them in gently.
Bake. Spread batter evenly in the pan. Bake for 20–28 minutes, until the top is set and a tester comes out with a few moist crumbs.
Cool and slice. Let cool in the pan for 10–15 minutes, then lift out and cool fully before slicing into bars.
Serve. Enjoy plain, or with a smear of almond butter or a drizzle of warm honey.