Mash the banana with a fork.
In a bowl, mix oatmeal, cocoa powder, and baking powder.
Add the mashed banana, egg, milk, and honey; mix to make a batter.
Chop dark chocolate into small pieces and mix it into the batter.
Pour the batter into a pan or oven-safe container and smooth the top.
Bake in a preheated oven at 180°C (356°F) for 20–25 minutes.