Preheat the oven to 180°C (356°F).
In a bowl, mix protein powder, almond flour, cocoa powder, and baking powder.
In another bowl, mash the banana, then add egg and unsweetened almond milk, and mix well.
Combine the wet and dry ingredients to make the batter.
Pour the batter into a pan lined with parchment paper.
Bake in the oven at 180°C (356°F) for 15–20 minutes.