1. Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or lightly grease it with cooking spray.

2. In a large bowl, whisk together the whole wheat flour, protein powder, baking powder, baking soda, salt, and cinnamon until evenly distributed.

3. In a separate medium bowl, mash the ripe bananas thoroughly until mostly smooth. Then, add the unsweetened applesauce, maple syrup (or honey), milk, egg, and vanilla extract. Whisk these wet ingredients together until well combined.

4. Pour the wet ingredient mixture into the bowl with the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are fine.

5. If using chopped nuts, seeds, or berries, gently fold them into the batter, distributing them evenly.

6. Divide the batter evenly among the 12 prepared muffin cups, filling each cup about two-thirds full.

7. Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back when lightly touched.

8. Remove the muffin tin from the oven and let the muffins cool in the pan for a few minutes before transferring them to a wire rack to cool completely.