Grind the oatmeal finely in a blender.
Combine eggs, banana, oatmeal, cocoa powder, baking powder, and milk in a bowl and mix well.
Pour the batter into a cake mold.
Bake in a preheated oven at 180°C (356°F) for 25 minutes.
After cooling, melt the chocolate using a double boiler and pour it over the cake.