Pre-heat your oven to 350F.
Prepare a 9 x 5 inch loaf pan with butter or spray it with baking spray. I line mine with parchment paper as well to make it easier to remove.
Mash bananas in the bottom of a large bowl.
Whisk in melted butter, add the brown sugar, egg, and vanilla.
Place baking soda, salt, flour and cocoa powder in a sifter and sift over wet ingredients.
Stir dry and wet ingredients with a spoon until just combined do not over mix as you do not want to bread to be dry.
Stir in chocolate chunks or chips.
Pour mixture in to prepared pan.
Bake for 55-65 minutes. Test for doneness with a toothpick or skewer that should come out clean and may have a smear of the chocolate chips.
Remove from oven and cool on a cooling rack.
Let cool for in pan for 15 minutes, then remove from pan and serve warm or cool completely.