Preheat oven to 350° F (180°C).
In a bowl, whisk eggs, banana, vanilla extract, coconut oil, cane sugar and peanut butter. Add coconut flour, cornflour, baking powder and mix until well-combined.
Pour batter into greased cake pan. Bake for 25-30 minutes.
Melt chocolate with 1 tbsp coconut oil. Allow the cake to cool before decorating with chocolate.