Preheat the oven to 350 degrees F.
Fill muffin tins with paper liners. This recipe makes about 24 muffins. Set the prepared pans aside.
Prepare the zucchini. Peel the zucchini and cut off about an inch at top and the bottom. See FAQs for thoughts on peeling.
Grate the zucchini using either a food processor or a box grater.
Place the grated zucchini in a double layer of paper towels and squeeze out most of the excess moisture. You may need to do this in more than one batch.
Put the grated zucchini in a small bowl and set aside.
Sift the flour and cocoa powder together in a large bowl. You can do first one and then the other.
Add the baking soda, cornstarch, and cinnamon to the flour mixture and whisk to combine. Set aside.
Add the granulated sugar, brown sugar, eggs, vanilla, and Greek yogurt to the bowl of a stand mixer fitted with a paddle attachment.
Beat on low speed until all of the ingredients are combined. It may look a bit chunky, but that is fine and will be fixed once you add in the dry ingredients.
Add the dry ingredients to the wet ingredients. Beat on low speed until just combined. Make sure to scrape the sides and bottom of the bowl with a rubber spatula. NOTE: Do not over mix your batter. Mixing until all of the ingredients are incorporated is all that is required.
Add the zucchini to the batter and stir to combine using a spatula or wooden spoon.
Add the chocolate chips and stir by hand to combine.
Using a small cookie scoop or a large spoon, fill each of the lined muffin cups about 2/3 full.
Bake for 20-24 minutes until a toothpick or wooden skewer inserted into the middle comes out clean.
Allow muffins to cool completely on a wire rack before eating.