Begin by preheating your oven to 350°F (175°C). Grease a 9x13-inch baking dish or line it with parchment paper for easier removal.
In a large mixing bowl, combine the granulated sugar, vegetable oil, and vanilla extract. Mix until smooth and well combined.
In a separate bowl, sift together the all-purpose flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, stirring continuously. The mixture might seem a bit dry at first.
Fold in the shredded zucchini. Let the batter sit for about 5 minutes. The zucchini will release moisture, making the batter more manageable.
Stir in the chocolate chunks or chips, ensuring they are evenly distributed throughout the batter.
Transfer the batter to the prepared baking dish, spreading it out evenly. Place in the oven and bake for 25-30 minutes or until a toothpick inserted into the center comes out with a few crumbs.
Once baked, remove from the oven and let it cool in the pan. Once cooled, slice into squares and serve!