Shred the zucchini and gently squeeze out excess moisture, leaving a little so the muffins stay soft.
Whisk together the flour, cocoa powder, baking soda, baking powder, salt, and cinnamon in a bowl.
In another bowl, whisk eggs, honey/maple syrup, oil, vanilla, and Greek yogurt.
Stir the shredded zucchini into the wet mixture.
Add the dry ingredients to the wet ingredients and stir just until combined.
Fold in the chocolate chips.
Preheat the oven to 350°F (175°C).
Line a muffin pan with paper liners or lightly grease it.
Fill each cup about ¾ full.
Bake for 18–22 minutes, or until a toothpick comes out clean (a bit of melted chocolate is okay).
Let the muffins cool in the pan briefly, then transfer to a rack to finish cooling.