Prep the pan and oven: Heat oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.

Mash bananas: In a large bowl, mash bananas until mostly smooth with a few small lumps for texture.

Whisk wet ingredients: Add eggs, Greek yogurt, oil, maple syrup or sweetener, and vanilla. Whisk until well combined and creamy.

Mix dry ingredients: In a separate bowl, stir together oat flour, almond flour, protein powder, baking soda, baking powder, salt, and cinnamon.

Combine gently: Add dry ingredients to wet. Stir with a spatula until just combined. The batter will be thick but scoopable. Do not overmix.

Add mix-ins: Fold in nuts, chocolate chips, or seeds if using. Keep total add-ins modest to maintain structure.

Fill the pan: Scrape batter into the prepared pan and smooth the top. If desired, sprinkle a few oats or nuts on top for a pretty finish.

Bake: Bake 45–55 minutes, until the center is set and a toothpick comes out with a few moist crumbs. If the top is browning too fast, tent loosely with foil at the 40-minute mark.

Cool fully: Let the loaf cool in the pan for 10 minutes, then lift out to a rack. Cool at least 1 hour before slicing so it sets and stays moist.

Slice and serve: Cut into 10–12 slices. Enjoy plain or with a thin spread of peanut butter for extra staying power.