Grease a 9 inch baking dish, preheat the oven to 350 degrees. Using a large mixing bowl, cream butter and sugar together. Add egg, vanilla, and bananas, beating thoroughly.In a separate bowl, combine flour, baking soda, baking powder, and salt. Add to creamed mixture and mix until the batter is smooth. Divide batter in half. To one half of the batter add the cocoa and mix til thoroughly incorporated. Spread the cocoa batter in the bottom of your prepared 9 inch greased baking dish.Spoon the remaining batter (without the cocoa) on top, swirling gently with butter knife if desired, and sprinkle with chocolate chips. Bake at 350 degrees for 30 minutes or until cake tests done with a toothpick. Cool the cake completely before slicing into servings.