Preheat oven to 350° and spray the bottom of a 9 x 5 baking dish with non stick spray.
In a large mixing bowl, beat sugar and butter together until smooth.
Beat eggs, bananas, buttermilk, vanilla into sugar mixture until well combined.
In a medium mixing bowl, whisk flour, baking soda, salt and cocoa powder together, then add to banana mixture and mix on low until combined.
Stir in chocolate chips.
Pour into prepared baking dish.
Bake for 1¼ hours, or until tooth pick inserted in the center comes out clean.
Remove from baking dish after 10 minutes and place on wire rack to cool.
Adapted from my Chocolate Chunk Banana Nut Bread