Prep the Zucchini. Grate the zucchini using a box grater. Don’t peel it. The green flecks disappear during baking. Lightly blot with a paper towel to remove excess moisture, but do not wring it dry. You want the natural moisture to help hydrate the batter.
Mix the Wet Ingredients. In a large mixing bowl, whisk together the oil, sugars, and vanilla extract until smooth and well combined.
Add the Dry Ingredients. Stir in the flour, cocoa powder, baking soda, and salt. The mixture may look dry at this point, but don’t worry! The zucchini will bring in the moisture.
Fold in the Zucchini. Add the grated zucchini and stir until a thick, rich batter forms. The moisture from the zucchini will loosen the mixture into a pourable consistency.
Add the Chocolate Chips. Fold in the chocolate chips. This step is optional but highly recommended for next-level gooey brownies.
Bake. Spread the batter into a greased or parchment-lined 8x8-inch baking pan. Bake at 350°F for 30–35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (but no wet batter).
Cool & Slice. Let the brownies cool completely in the pan before slicing. This allows them to set for clean cuts and maximum fudginess.