Preheat oven to 375 degrees F. Spray a muffin tin with nonstick spray or line with muffin liners. Set aside.
In a large bowl whisk together flour, cocoa powder, sugars, baking powder, baking soda, and salt.
Add the egg, melted butter, and vanilla extract. Add skim milk and stir until combined. Fold in shredded zucchini and chocolate chips (batter will be thick).
Divide batter evenly between the prepared muffin cups and place in the oven. Bake for 20-25 minutes or until a toothpick inserted in the middle comes out clean. Remove from the oven and let muffins cool in muffin pan until theyโre safe to handle, about 10 minutes. Transfer to a wire rack to cool completely.