Preheat the oven to 180°C (356°F).
Mash the banana.
Combine the egg, cocoa powder, banana, Greek yogurt, and protein powder in a bowl and mix well.
Add baking powder and mix evenly.
Line a pan with parchment paper and pour in the batter.
Bake at 180°C (356°F) for 20-25 minutes.
Let it cool before serving.