Preheat oven to 350℉
In a bowl, whisk flour, cocoa powder, baking soda, salt and cinnamon. Set aside.
Using a hand or stand mixer, mix egg, oil, sugar and vanilla until combined.
Gradually add dry ingredients into the wet mixture and mix until combined (do not overmix).
Fold grated zucchini and chocolate chips.
Add the batter to a muffin tin (lined or greased), fill each ¾.
Bake for about 20 minutes or until a toothpick comes out clean.
Let them cool.
Optional : drizzle some chocolate on top.