Preheat the oven to 350°F, and line a 9x5 loaf pan with parchment paper.
Grate the zucchini, measure out the correct amount, then lay out on paper towels to blot dry. I let mine stay on the paper towels while I prep the rest of the batter so it continues to seep out moisture. You don't want it bone dry, but also if it's too wet it could alter the consistency of the batter.
Make the vegan buttermilk by measuring out ¾ cup non-dairy milk, then adding 1 tsp of vinegar. Let it sit for a few minutes to curdle.
While the buttermilk is curdling, in a large bowl mix together flour, cornstarch, cocoa powder, salt, and baking powder. See notes below or more details throughout the post about how to swap out the cornstarch, or use some Dutch cocoa powder in place of a little bit of the regular cocoa powder.
Separately whisk together vegan buttermilk, neutral oil, applesauce, and vanilla extract. Add in sugar and whisk again until smooth, then add the wet ingredients into the dry and mix until just combined.
Finally, add in the zucchini (and chocolate chips or nuts if you are using any), and mix until evenly distributed throughout the batter. Try not to overmix or the batter will get tough!
Pour the batter into the lined loaf pan and stick into the oven. Bake for 55-60 minutes, testing for doneness by sticking a toothpick into the middle part of the loaf and making sure it comes out with crumbs, not wet batter.
Once done, remove the pan from the oven and stick it onto a cooling rack. Let the cake continue to firm and cool inside the pan for an hour before removing to further cool, or eat while it's warm.
Eat and enjoy!