Ingredients
Method
Place a rack in middle of oven; preheat to 325°. Coat a 9x5" loaf pan with nonstick vegetable oil spray and line with parchment paper, leaving generous overhang on long sides. If using, toast 1 cup (115 g) walnuts on a small rimmed baking sheet, toasting halfway through, until golden brown, 8–10 minutes. Let cool, then coarsely chop.
Whisk 2 large eggs, 1 cup (packed; 200 g) light brown sugar, ¾ cup vegetable oil, ½ cup (32 g) Dutch-process cocoa powder, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, 2 tsp. vanilla extract, and 1 tsp. ground cinnamon in a large bowl until smooth, about 2 minutes. Vigorously whisk in ½ tsp. baking powder and ½ tsp. baking soda.
Add 1 lb. zucchini (about 4 small), scrubbed, grated on the large holes of a box grater, to batter and stir to combine. Add 1½ cups (188 g) all-purpose flour, 1 cup (190 g) semisweet chocolate chips, and walnuts (if using) and stir again just until no large dry streaks of flour remain. Scrape batter into prepared pan. Sprinkle 2 Tbsp. raw or granulated sugar evenly over top.
Bake zucchini bread, rotating pan front to back halfway through, until a tester inserted into the center comes out clean (an instant-read thermometer inserted into the center should registers 200°), 60–80 minutes. Transfer pan to a wire rack and let bread cool in pan. Run a small offset spatula or knife around sides of bread to help loosen, then turn out onto a platter. Do ahead: Bread can be baked 2 days ahead. Store uncut bread loosely covered at room temperature. Once sliced, store airtight and chill.