Preheat oven to 350°F (175°C) and grease a 9x5 inch loaf pan with non-stick spray.

In a large mixing bowl, whisk together mashed bananas, eggs, Greek yogurt, egg whites, and vanilla extract until homogeneous.

In a separate bowl, combine whole wheat flour, whey protein powder, baking soda, salt, and cinnamon.

Gently fold the dry ingredients into the wet mixture using a spatula until no dry streaks remain; avoid overmixing to prevent a rubbery texture.

Transfer the batter into the prepared loaf pan and level the surface.

Bake for 45 to 55 minutes, or until an internal temperature of 200°F (93°C) is reached or a skewer comes out clean.

Cool in the pan for 10 minutes before transferring to a wire rack for complete cooling.

Slice into 10 equal portions to ensure 10g of protein per serving.