Preheat the oven to 180°C (356°F).
In a bowl, mix together the protein powder, cocoa powder, baking powder, and oatmeal.
In another bowl, add eggs, milk, and banana, then mash and mix well.
Combine the mixtures from both bowls and mix thoroughly.
Add dark chocolate or chocolate chips and mix evenly.
Divide the batter into a muffin pan.
Bake in the oven for 15–20 minutes.