Add the milk (if it's cold it will help the mix cool down), the egg, honey, vanilla essence and mix. Finish with the dry ingredients and mix again.
For the marbled half
Divide the dough in two and add the cocoa powder and milk to one of them.
For the chocolate chunks
Add half of the chunks to one of the doughs and the other half to the other.
Place both dough in a bowl and give it one or two mixing movements with a spatula to marble.
Put baking paper inside the mould because if there's a bit of banana on the side it could make the bread stick to the mould. You could put it in as it fits or you could draw with a pencil on the paper tracing the shape of the base and sizes and cut it perfectly to size. Remember to have the pencil trace towards the mould and not the dough. The second technique will achieve perfect edges.
Put the mix inside the mould.
Choose a banana a bit less long than the mould and cut it lengthwise. This is laid on top of the dough with the inside facing upward as an optional garnish.
Bake the banana bread at 170C for 1 hour or until you put a thin knife at the center and it comes out clean.