Preheat the oven to 350 degrees. Grease a 12-count muffin tin.
In a large bowl, combine the bananas, cinnamon, vanilla, oil, egg, and brown sugar. Mix well.
Add the flour, protein powder, baking powder, baking soda, and salt. Stir the ingredients until just combined.
Add the milk and mix until everything is combined. Fold in the chocolate chips.
Pour the batter evenly into each spot in the muffin tin, filling almost completely. Bake for approximately 20 minutes, or until muffins are golden brown on top and a knife pulls out clean. Let cool for a few minutes in the pan, then remove from the pan and allow to finish cooling. Enjoy.