Preheat the oven to 350 F or 180 C and grease a 9x5 inch loaf pan with butter or non-stick spray.

In a medium sized bowl, mash the bananas.

Stream in the melted butter and whisk to combine.

Next, add in the brown sugar, followed by the egg and vanilla extract.

Mix after each addition and make sure that all the ingredients are well-incorporated.

Whisk in the baking soda, salt, cinnamon.

Once incorporated, add in the cocoa powder, making sure there are no lumps. You can sift the mixture if you'd like.

Then add the flour, mixing just until combined. You can also stir all the dry ingredients in a separate bowl and then add them to the wet mixture.

Fold in the chocolate chunks and nuts.

Pour into the prepared ban and bake for 50 minutes or until a toothpick comes out clean.

Cool slightly before slicing.