Preheat the oven to 175 C.
Mash the bananas finely.
Add the self-raising flour and baking powder.
Melt the margarine in a saucepan. Meanwhile, beat eggs with a mixer.
Add the margarine, eggs, vanilla extract, and milk.
Split 1/3 of the dough and add the cocoa.
Place a layer of vanilla banana mix in the baking tin. Place 2 stripes of chocolate banana mix on top. Repeat until it's gone.
Cut the hazelnuts in half and sprinkle them on the cake along with the chocolate chips.
Put the mix in the oven for 45-50 minutes.
Let it cool for 10 minutes.