Preheat oven to 375 degrees F. Line a muffin tin with muffin liners, or grease well.
In a medium bowl, make the flax egg by combining the ground flaxseed with water. Stir and set aside for 5 minutes to thicken.
In a liquid measuring cup, add the almond milk and apple cider vinegar. Stir and set aside to curdle. This is your vegan buttermilk.
In a large bowl, add the flour, cacao powder, salt, baking soda, baking powder, and sugar. Whisk until well combined.
In the bowl with the flax egg, add the almond milk mixture, shredded zucchini (making sure you squeeze out the excess liquid), pure maple syrup, and vanilla. Whisk until well combined.
Add the wet to the dry ingredients. Use a spatula and stir until just combined. Careful not to overmix! Fold in chocolate chips.
Divide batter into muffin tins, filling them up almost all the way to the top. Sprinkle extra chocolate chips on top. Bake for 15-18 minutes, or until a toothpick inserted in the middle comes out mostly clean. Let it cool in the pan for 10 minutes, then carefully remove muffins and place on a wire rack to cool completely. Enjoy! Store leftover muffins in an airtight container on the counter for up to 3 days. It will be even more moist/flavorful the next day.