01 - Set oven to 350°F. Lightly grease a 9x9-inch baking dish with oil or nonstick spray.
02 - In a large bowl, whisk together the flour, protein powder, sugar, baking powder, baking soda, and salt.
03 - In a separate bowl, whisk milk, eggs, melted coconut oil or butter, and vanilla extract until thoroughly combined.
04 - Add wet mixture to dry ingredients and stir gently until just incorporated. Avoid overmixing to maintain tenderness.
05 - Carefully fold in banana slices and mixed berries until evenly distributed throughout the batter.
06 - Transfer batter into the prepared dish and smooth the surface with a spatula. Sprinkle sliced almonds or pecans over the top, if desired.
07 - Place dish in oven and bake for 30–35 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
08 - Allow bake to cool for 10 minutes before slicing. Serve warm with a drizzle of maple syrup if preferred.