Preheat your oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan, or line it with parchment paper for easier removal.
In a large mixing bowl, combine the all-purpose flour, whole wheat flour, cocoa powder, baking powder, baking soda, salt, and cinnamon. Whisk the dry ingredients together until evenly mixed.
In another bowl, whisk together the granulated sugar, brown sugar, eggs, vegetable oil, and vanilla extract until well combined and smooth.
Add the grated zucchini into the wet mixture and stir until fully incorporated.
Gradually fold the wet mixture into the dry ingredients using a rubber spatula. Be careful not to overmix; a few lumps are okay.
If desired, gently fold in the semi-sweet chocolate chips.
Pour the batter into the prepared loaf pan, spreading it evenly.
Bake in the preheated oven for 50 minutes, or until a toothpick inserted into the center comes out clean.
Remove the loaf from the oven and let it cool in the pan for about 10 minutes before transferring it onto a wire rack to cool completely.