Preheat your oven to 350°F (175°C).
Line a 12-cup muffin tin with paper liners or lightly grease it.
In a large bowl, mash the bananas until mostly smooth. Whisk in the eggs, Greek yogurt, maple syrup, vanilla, and oil if using until well combined.
In a separate bowl, whisk the white whole wheat flour, oat flour, protein powder, baking powder, baking soda, salt, and cinnamon.
Pour the dry ingredients into the wet ingredients. Stir gently with a spatula until just combined.
If the batter seems very thick or dry, add the milk 1 tablespoon at a time until it resembles a thick, scoopable batter.
Fold in the chocolate chips, reserving a small handful for the tops.
Divide the batter evenly among the muffin cups, filling each about 3/4 full. Sprinkle a few extra chocolate chips on top for that bakery look.
Bake for 16–20 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs (avoid chocolate spots when testing).
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely. The muffins set up as they cool, so try not to dig in too early.