Preheat oven to 375 degrees F and spray non-stick 12 muffin tin with cooking spray. Set aside.
In a large mixing bowl add egg, applesauce, maple syrup, milk, oil, vanilla extract, baking powder, baking soda and salt; whisk well to combine. Add cacao powder and whisk until no lumps are left.
Add zucchini and stir. Add flour and gently mix just until combined. Do not over mix. Fold in chocolate chips.
Distribute batter evenly between 12 openings of a tin (I used regular ice cream scoop) and bake for 23 minutes or until a toothpick inserted in the center comes out clean.
Let muffins cool for a few minutes and transfer to a cooling rack to cool off completely.
Notes
Store: Day 1-2 covered with a towel on a counter. After refrigerate in a glass airtight container for 2-3 more days. Freeze for up to 3 months.
Swap the applesauce: For the same amount of mashed bananas for a slightly different flavor. Or replace with yogurt but muffins will be less sweet, which in this case is OK because these are sweeter muffins.
No need to peel zucchini first. The skin is thin, light, and edible.
Mini muffins: Cut baking time in half, check for doneness and either remove or add 1 -2 minutes extra time.