Preheat oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large bowl, mash the bananas until smooth.
Whisk in the eggs, Greek yogurt, maple syrup, and vanilla extract until well combined.
In a separate bowl, whisk together the oat flour, protein powder, baking soda, salt, and cinnamon.
Gradually fold the dry ingredients into the wet ingredients until just combined; do not overmix.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 45 to 55 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.