Preheat oven to 350°F and prepare a 9x13" pan with baking spray and line with parchment paper.
In a large bowl combine oil, sugar, and vanilla until fully incorporated.
Add flour, cocoa, baking soda and salt. Mix until combined. NOTE: the batter will be very dry.
Fold in zucchini by hand. Allow batter to rest for 5-10 minutes.
Add in chocolate chunks and stir again. Batter should appear wet. If it’s not wet, let it stand for 5 more minutes and stir again.
Spread brownie mixture into the pan and bake for 25-35 minutes. Brownies are done with an inserted toothpick is removed with crumbs. There shouldn't be wet batter on the toothpick