- Preheat your oven to 350-f degrees. Butter and flour two loaf sized pans. Prepare the topping and set aside. 
- In a bowl, whisk together the flour, cinnamon, baking soda, salt and cocoa to remove any clumps and to incorporate fully. 
- In another bowl, beat together the oil, sugar, brown sugar and eggs for 2 minutes. A hand mixer is handy but I mixed by hand and it worked fine. 
- Add the vanilla and sour cream to the egg mixture. Stir to combine. 
- Gently stir in the zucchini and orange zest to the egg mixture. 
- Toss the chocolate chips with a spoonful of flour (this helps to stop them from sinking to the bottom of the bread). 
- Add the flour to the egg mixture, gently folding it in and being careful not to overmix. Add chocolate pieces. 
- Pour the mixture evenly between the two pans. Top with the sugar and cinnamon mixture. 
- Bake for 50-60 minutes until a toothpick or sharp knife inserted can be removed cleanly. Cool for 10 minutes then remove from pan and set on a cooking rack or dish.