Preheat the oven to 180°C (355°F).
Mash the banana with a fork.
In a bowl, combine the mashed banana, protein powder, cocoa powder, oatmeal, almond milk, baking powder, and egg. Mix well.
Lightly grease a pan with oil.
Pour the batter into the pan.
Bake in the preheated oven for 25-30 minutes.
Let it cool on a wire rack before serving.