1. Preheat the oven to 350°F (175°C). Grease or line a 9×13-inch baking pan with parchment paper, leaving an overhang on the long sides so you can lift the brownies out after baking.

2. Finely shred the zucchini using the small holes of a box grater. Lightly blot the shredded zucchini with a clean kitchen towel or paper towel to remove only excess surface moisture; do not squeeze it completely dry.

3. In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until well combined and no streaks of cocoa remain.

4. In a large mixing bowl, whisk the melted butter, granulated sugar, and brown sugar until glossy and fully blended.

5. Add the eggs one at a time, whisking well after each addition until the mixture thickens slightly and looks smooth.

6. Whisk in the vanilla extract and the instant espresso powder or cooled coffee, if using, until evenly incorporated.

7. Switch to a rubber spatula and fold the shredded zucchini into the wet mixture, spreading it out so it is evenly distributed.

8. Add the dry ingredients to the wet ingredients and gently fold just until no dry pockets of flour remain; avoid overmixing so the brownies stay fudgy.

9. Fold in about 3/4 cup of the chocolate chips, reserving the remaining 1/4 cup for the top.

10. Scrape the batter into the prepared pan and spread it into an even layer with the spatula. Sprinkle the reserved chocolate chips over the surface.

11. Bake for 28–32 minutes, or until the edges are set and a toothpick inserted near the center comes out with a few moist crumbs but no wet batter. Begin checking at 26 minutes, as ovens vary.

12. Place the pan on a wire rack and let the brownies cool completely in the pan to finish setting and make clean slices easier.

13. Once cool, use the parchment overhang to lift the brownies out of the pan. Transfer to a cutting board and slice into 16 to 20 squares, wiping the knife between cuts for neat edges.

14. Serve at room temperature or slightly warmed. Store leftovers in an airtight container at room temperature for up to 3 days, refrigerate up to 5 days, or freeze well-wrapped squares for up to 2 months.