Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large mixing bowl, combine the mashed bananas, Greek yogurt, honey (or maple syrup), applesauce, eggs, and vanilla extract. Mix until well combined.
In another bowl, whisk together the almond flour, protein powder, baking soda, salt, and cinnamon.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.
If desired, fold in the chopped walnuts for added texture.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for 50-60 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 it to a wire rack to cool completely.