Coat an 8×5-inch loaf pan with cooking spray and preheat the oven to 350°F.

In a large bowl, cream together 8 tablespoons room temperature unsalted butter and 1 cup granulated sugar until light and fluffy, then beat in the eggs one at a time until completely combined. Stir in 1/2 cup unsweetened cocoa powder, 2 teaspoons baking powder, 1 teaspoon pure vanilla extract, and 1/4 teaspoon kosher salt. Fold in 2 cups coarsely grated zucchini, then add 1 1/3 cups all-purpose flour and 1/2 cup semisweet chocolate chips to the bowl. Stir until just combined.

Transfer to the loaf pan and spread into an even layer. Bake until a toothpick inserted into the center of the loaf comes out clean (although there might be some melted chocolate on it from the chocolate chips), 50 to 60 minutes. Let the bread cool in the pan for 10 minutes. Flip out onto a wire rack and cool completely before slicing and serving.