Preheat oven to 350°F and prepare a 9×13 pan with butter (or use baking spray) and line with parchment paper. (Allow parchment paper to go up the sides for easy removal.)
In a large bowl combine oil, sugar, eggs, and vanilla until fully incorporated.
Add flour, cocoa, baking soda, and salt. Mix until combined, the batter will be very dry.
Fold in zucchini. Allow batter to rest for 5 minutes.
Add in chocolate chunks and stir again. Batter should appear more wet.
Spread brownie mixture into the pan and bake for 35 minutes Brownies are done when sides are set but centre is still jiggly. Let fully cool.
