Preheat the oven to 375-degrees F. Spray two 9 x 5-inch bread loaf pans with cooking spray or line with paper liners. (This makes cleanup very easy)
In a large mixing bowl, using an electric hand mixer, whisk or wooden spoon, combine the sugar, brown sugar, eggs, sour cream, oil and vanilla extract to the mixture and combine.
Add the flour, cocoa powder, espresso powder, baking soda, baking powder, and salt, stirring to combine.
Once mixed thoroughly, fold in the grated zucchini and chocolate chips with a rubber spatula. The batter will be thick.
Divide batter evenly into two prepared (9x5-inch) loaf pans. Place the baking pans on a half sheet pan, lined with parchment paper. (This helps catch any dropped batter and helps easily rotate pans.) Bake for 8-10 minutes and LOWER the temperature to 350-degrees F.
Rotate your breads once through the baking process, so they bake evenly. Carefully rotate the entire half sheet pan 180-degrees about three quarters through the baking process. (Be very careful not to bump the pans or your bread will fall!!)
Bake for 65-70 minutes, or until a toothpick when inserted comes out mostly clean with a few moist crumbs. Towards the end of the baking process, monitor the loaves and rotate them a few times. (Every oven is different, so your loaves may take a few extra minutes)
Remove loaves from the oven. Let cool in the baking pans for 10-15 minutes. Turn out of baking pans, place chocolate zucchini breads on a wire cooling rack to cool completely.
Once cooled, package into plastic bread bags with a twist tie.