Start by washing and finely grating 1 cup of zucchini. Place the grated zucchini in a clean kitchen towel or paper towels and gently squeeze out excess water. This step is crucial to avoid soggy brownies.
In a large bowl, whisk together the granulated sugar, brown sugar, and vegetable oil until fully combined. Beat in the eggs one at a time, then stir in the vanilla extract.
In a separate bowl, sift together the all-purpose flour, cocoa powder, baking powder, baking soda, and salt. This ensures even distribution and prevents lumps.
Gradually add the dry ingredients into the wet mixture, folding gently until just combined. Avoid overmixing to keep brownies tender. Then fold in the grated zucchini and chocolate chips, distributing them evenly throughout the batter.
Preheat your oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper or grease it well. Transfer the brownie batter into the pan, spreading it evenly. Bake for 25-30 minutes or until a toothpick inserted near the center comes out with moist crumbs.
Allow the brownies to cool completely in the pan on a wire rack. Once cooled, lift them out using the parchment paper edges and cut into squares. These brownies are perfect served with a glass of cold milk or a scoop of vanilla ice cream.