Shred zucchini with a box grater to make 2 cups, packed down just a little. Measure out the walnuts.
In a mixing bowl, add the flour, cocoa, baking soda, and salt. Whisk together.
Preheat your oven to 190° C (375° F), get out a 9x13 inch baking pan and grease with butter or cooking spray, and flour it.
In another mixing bowl, add the oil, sugar, and vanilla. Mix together.
Add the flour mixture to the sugar mixture and mix together, it will be quite dry.
Add the zucchini and walnuts, mix together. it will seem a dry, just keep mixing and it will come together with a shiny or wet appearance. If your mixture is drier than what this photo shows, mix in a tablespoon of water. The mixture will be much drier than a regular brownie mix, as it cooks, the zucchini will release moisture.
Spread mixture into prepared baking pan evenly.
Bake for 25-30 minutes or until the top springs back up after gently pressed.
Cut into squares, serve and enjoy.