Preheat the oven to 325ºF (167ºC). Butter a 9X5-inch loaf pan or spray with nonstick cooking spray. Fit with a sling made out of foil or parchment paper. Set aside.
Add eggs, brown sugar, oil vanilla, and salt to a large mixing bowl then whisk vigorously (by hand) until the mixture is smooth and glossy, about 30-45 seconds.
Mix in grated zucchini stirring until evenly incorporated.
Set a large sieve over the mixing bowl and sift in flour, cocoa, baking powder, baking soda, and espresso powder directly over the egg mixture. Use a large rubber spatula to gently stir mixture, removing any air pockets, being careful to not to overmix.
Remove and set aside 1 tablespoon of chocolate chips. Add the remaining chocolate chips and fold until they're evenly distributed in batter.
Pour batter into prepared loaf pan. Sprinkle the top of the batter with coarse sugar and reserved chocolate chips, gently pressing them in slightly, to the top of the batter.
Bake the loaf in preheated oven, for 75-80 minutes, or until a bamboo skewer inserted into the center of the loaf comes out clean.
Allow the loaf to cool in loaf pan for 15 minutes. Use the sling, remove loaf to a wire baking rack, and cool completely before slicing, about 2 hours.