Preheat oven to 350 degrees. Line or lightly spray one standard size muffin tin, set aside.
In the bowl of a stand mixer, beat together sugars and oil for 30 seconds. Add sour cream, milk, vanilla and egg, mix until just combined.
In a medium size mixing bowl, whisk together flour, baking powder, baking soda, cocoa powder, and salt. With mixing speed on low, gradually add dry ingredients until the mixture becomes smooth and no flour pockets remain.
Remove bowl from stand and fold in zucchini (I used the smaller “cheese” holes on my grater for the zucchini, the large ones would have been too thick and chunky) and chocolate chunks. Scoop batter into prepared muffin tin, filling each ¾ of the way full. Top with additional chocolate chunks.
Place in oven and bake for 16-18 minutes or until the tops spring back. Remove from oven and allow to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.