Preheat oven to 175 degrees Celsius (350 degrees Fahrenheit) and line an 8x4 inch loaf pan with parchment paper.

In a large mixing bowl, mash the bananas until a smooth consistency is achieved with minimal lumps.

Whisk in the Greek yogurt, liquid egg whites, and vanilla extract until the wet base is homogeneous.

In a separate container, sift together the oat flour, protein powder, cocoa powder, sweetener, baking soda, baking powder, and salt.

Incorporate the dry ingredients into the wet mixture using a spatula, folding gently until just combined to avoid toughening the crumb.

Pour the batter into the prepared loaf pan and level the surface with a spatula.

Bake for 40 to 45 minutes, or until a wooden skewer inserted into the center emerges clean or with only a few dry crumbs.

Allow the loaf to cool in the pan for 15 minutes before transferring to a wire rack to cool completely before slicing into 10 portions.