Set the oven to 200 degrees Celsius (392 degrees Fahrenheit).

Blend banana, oats, cocoa, eggs, honey, and baking powder thoroughly with a hand blender or in a food processor.

Pour the batter into a pan about 30 x 30 cm lined with baking paper.

Bake the cake in the oven at 200 degrees Celsius (392 degrees Fahrenheit) for about 25 minutes.

Take the cake out of the oven and let it cool.

Break the chocolate into smaller pieces and put them in a small heatproof bowl.

Place the bowl over a pot of boiling water until the chocolate has melted.

Spread the chocolate on the cake.

Serve the cake once the chocolate has hardened.