Preheat your oven to 350ºF, and grease two 8x4-inch loaf pans. You can optionally flour them or line them with a sheet of parchment paper for easier release.
In a small bowl, dissolve the cocoa powder in the boiling water.
In a large bowl, whisk together the flour, sugar, cinnamon, baking soda, and salt. Add the oil, milk beverage, vanilla, dissolved cocoa powder, and zucchini and stir until just combined. Fold in the blueberries or chocolate chips and walnuts (if using).
Divide the batter equally between the loaf pans and even it out.
Bake for 55 minutes or until a toothpick inserted in the center of a loaf comes out clean (although it might have some chocolate or blueberry on it if you used those additions).
Notes
Marbled Loaf Option: Before adding the dissolved cocoa powder, remove 1 cup of batter from the large bowl and transfer to smaller bowl. Add the cocoa to the small bowl and stir to combine. Alternate scoops of the plain batter and cocoa batter in each loaf pan, and use a butter knife to swirl a figure eight in the batter before placing the pans in the oven.
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/dairy-free-egg-free-chocolate-zucchini-bread