Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, salt, and cinnamon until well combined.
In another bowl, mix the vegetable oil, eggs, and vanilla extract until smooth.
Add the grated zucchini to the wet ingredients and stir until evenly combined.
Pour the wet mixture into the dry ingredients and gently fold until just combined. Be careful not to overmix.
Fold in the chocolate chips until evenly distributed throughout the batter.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.