Preheat oven at 350⁰F/177⁰C. Grease, line with non-stick paper a 9x5-inch loaf pan. Set aside.
In a bowl, mix together banana cake mix, oil, water and mashed bananas. Set aside.
In another bowl, mix together chocolate cake mix, oil, water and mashed bananas.
Pour the cake mixes unto the prepared pan alternately to make a marbled loaf. Using a toothpick, make swirl patterns on top of the loaf.
Bake in the preheated oven for 25-30 minutes or until set. Serve.