Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease the cups.
In a large mixing bowl, combine the mashed bananas, eggs, unsweetened applesauce, honey, and vanilla extract. Whisk until smooth and well combined.
In a separate bowl, whisk together the whole wheat flour, vanilla whey protein powder, baking powder, baking soda, salt, and ground cinnamon.
Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Do not overmix.
Fold in the plain Greek yogurt until evenly distributed in the batter.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.