Preheat the oven to 180°C (356°F).
In a bowl, mix the protein powder, oat flour, baking powder, and cocoa powder.
In another bowl, mash the banana and combine with egg, almond milk, honey, and coconut oil.
Combine the dry and wet ingredients, mixing thoroughly.
Pour the batter into a baking pan and spread evenly.
Bake in the preheated oven for 20–25 minutes at 180°C.
Let it cool and cut into pieces.