1. Preheat oven to 350°F. Lightly grease an eight-inch loaf pan.
2. In a large bowl, mash the bananas with a fork. Mix in the sugar, oil, nondairy milk, and vanilla.
3. Add the white whole-wheat flour, protein powder, baking soda, and salt, and mix until just combined.
4. Now it's time to make the chocolate batter. Scoop out one cup of the banana bread batter into a small glass measuring cup or other heatproof bowl. Add the cocoa powder and three tablespoons of the boiling water (you'll use the other three in a second). Mix until a silky chocolate batter forms. Set aside.
5. Add the remaining three tablespoons of boiling water to the original batter, and mix until smooth.
6. Ready to get creative? Drop a large spoonful of the regular batter into your prepared pan. Now drop a large spoonful of the chocolate batter. Continue alternating between the two until all the batter is in the pan.
7. Now for the marbling! Poke a butter knife into the batter, and swirl it around about six times; don't overdo it, because you want to maintain the two separate flavors. Toppings are optional.



8. Bake it for 45 to 50 minutes or until a toothpick inserted in the center comes out clean.
9. Store leftovers in an airtight container in the fridge for up to five days, or freeze.

Here's the nutritional info for one piece (makes eight):