In a large bowl, cream together the butter, granulated sugar, and brown sugar.
Mix in the mashed bananas and vanilla extract.
In a separate bowl, mix together the flour, cocoa powder, baking powder, baking soda.
Fold the flour mixture into the banana mixture until incorporated.
Pour into the greased loaf pan. Sprinkle chocolate chips on top.
Bake for 45-55 minutes, or until a toothpick comes out clean.
After removing from the oven, let the bread cool for about 30 minutes and then remove from the pan. I usually give my pan a few good taps on the counter to loosen it up. Then let cool completely on rack.