Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or grease lightly.
In a large bowl, mash the bananas until mostly smooth. Whisk in the eggs, Greek yogurt, milk, oil, vanilla, and sugar until well combined.
Sprinkle the protein powder over the wet mixture and whisk until no lumps remain.
This helps it integrate smoothly.
In the same bowl, add the oat flour, whole wheat (or all-purpose) flour, baking powder, baking soda, cinnamon, salt, and optional flaxseed. Stir gently with a spatula until just combined.
Fold in the chocolate chips. The batter should be thick but scoopable.
If it’s too stiff, add 1–2 tablespoons of milk.
Divide the batter evenly among the muffin cups. Top with a few extra chocolate chips for looks.
Bake for 16–20 minutes, or until the tops are set and a toothpick comes out mostly clean (a little melted chocolate is fine).
Cool in the pan for 5 minutes, then transfer to a wire rack. Let them cool fully for the best texture.