Preheat the oven to 350°F. Lightly spray a 9×5-inch loaf pan with non-stick spray.
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, salt, and espresso powder until well combined.
In a medium bowl, whisk together brown sugar, granulated sugar, oil, vanilla, and eggs until smooth.
Pour the wet mixture into the bowl with the dry ingredients, stirring gently until just combined. (The batter will be thick.)
Fold in the grated zucchini and chocolate chips until evenly distributed, being careful not to overmix.
Pour the batter into the prepared loaf pan, smoothing the top with a spatula.
Place the pan in the oven, then immediately reduce the temperature to 325°F.
Bake for 80-90 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs, but no raw batter. If the top is browning too quickly, loosely cover the loaf with aluminum foil during the last 10–15 minutes of baking.
Allow the bread to cool in the pan for about 15 minutes, then transfer to a wire rack to cool completely before slicing and serving.