Preheat oven to 350°F. Grease 24 muffin cups. Whisk sugar, eggs, oil, zucchini, and vanilla in a large bowl.
Combine flour, baking soda, baking powder, cinnamon, cocoa, salt, and chocolate chips in a medium bowl; mix well.
Add flour mixture to zucchini mixture; whisk just until blended.
Spoon batter into prepared muffin cups. Bake until a toothpick inserted in center of muffins comes out clean, about 20 minutes.
Note: For perfectly round muffin tops that will not spread, grease the bottom and only halfway up the side of each muffin cup.
