Preheat the oven to 350°F, or 177°C. Grease a 9 × 13-inch baking pan and line the bottom with parchment paper if desired.

Wash and trim the zucchini. Finely shred it using a box grater. Gently blot excess moisture with a clean kitchen towel, but do not squeeze the zucchini completely dry.

In a medium bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt.

In a large mixing bowl, whisk together the vegetable oil, granulated sugar, brown sugar, eggs, sour cream, and vanilla extract until smooth.

Stir the shredded zucchini into the wet ingredients.

Add the dry ingredients to the wet mixture. Gently stir with a rubber spatula until just combined. Do not overmix.

Fold in the chocolate chips, reserving a few to sprinkle over the top if desired.

Spread the batter evenly into the prepared baking pan.

Bake for 40–50 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.

Place the cake on a cooling rack and let it cool completely before slicing or adding frosting.

Serve plain, dusted with powdered sugar, or topped with chocolate frosting or chocolate ganache.