Preheat and prep: Heat the oven to 400°F (200°C). Line a rimmed sheet pan (about 13x18 inches) with parchment and lightly grease the sides.

Make oat flour: If using rolled oats, blend 2 cups until finely ground. You can also use 2 cups store-bought oat flour.

Whisk dry ingredients: In a large bowl, combine 2 cups oat flour, 2 scoops protein powder (about 50–60 g), 2 teaspoons baking powder, 1/2 teaspoon salt, and 1 teaspoon cinnamon.

Blend wet ingredients: In another bowl, mash 2 ripe bananas. Whisk in 3 eggs, 1 cup Greek yogurt, 1 cup milk, 2–3 tablespoons maple syrup, and 1 teaspoon vanilla.

Combine: Pour wet into dry. Stir gently until just combined. The batter should be thick but pourable. If too thick, add a splash more milk.

Add mix-ins: Fold in 1–1.5 cups of blueberries, chocolate chips, or nuts if you like. Don’t overmix.

Pan and smooth: Pour the batter onto the prepared sheet pan. Spread evenly to the corners with a spatula for uniform baking.

Bake: Bake for 12–16 minutes, until set in the center and lightly golden at the edges. A toothpick should come out clean.

Cool and slice: Let cool 10 minutes. Lift with the parchment and transfer to a cutting board. Slice into squares or bars.

Serve or store: Enjoy warm now, or cool completely before packing for meal prep.