Preheat oven to 350F and lightly spray muffin with oil.
Mix flax egg in a small bowl and set aside. Grate zucchini using a grater box (regular grate size). Set aside.
Mix almond milk and apple cider vinegar (or sub fresh lemon juice) in a small bowl and set aside. It will curdle, but this is the point in order to make vegan buttermilk.
In a large mixing bowl, mix together the dry ingredients (flour, cocoa powder, baking powder, baking soda, salt, and sugar).
Mix together the wet ingredients (flax egg, almond milk mixture, maple syrup, and vanilla) and then pour over dry ingredients. Stir until just combined. Fold in the chocolate chips, walnuts, and shredded zucchini.
Spoon batter into prepared muffin tin filling each tin 3/4 of the way full. Bake for about 15-17 minutes at 350F, or until muffins slowly spring back when touched. A toothpick should come out mostly clean. Cool in tin for 5 minutes. With a knife, loosen around the muffin edge and transfer to a cooling rack until completely cool.
Serve and enjoy!