Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
Prepare the Zucchini: Grate the zucchini and then squeeze out any excess moisture using a clean kitchen towel or paper towels.
Mix Dry Ingredients: In a medium mixing bowl, whisk together the flour, cocoa powder, baking soda, baking powder, salt, and cinnamon (if using).
Mix Wet Ingredients: In a large bowl, beat the eggs, sugar, olive oil (or melted butter), and vanilla extract until smooth.
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the wet mixture, stirring gently until just combined. Avoid overmixing. Add Zucchini and Chocolate Chips: Fold in the grated zucchini and chocolate chips, ensuring they are evenly distributed throughout the batter.
Bake the Bread: Pour the batter into the prepared loaf pan. Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean with a few moist crumbs. If the top is browning too quickly, cover it with aluminum foil. Cool: Let the bread cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
Serve: Slice and serve once completely cooled.