Spray a 9x13 baking pan with Baker's Joy and line with parchment paper. Set aside. Preheat oven to 350℉.
In a large bowl, beat oil, sugar, and vanilla together for 2- 3 minutes.
In a medium bowl, sift together the flour, cocoa powder, baking soda, and salt. Whisk to combine.
Stir the dry ingredients into the sugar mixture in two or three batches.
Fold in the zucchini and nuts (if using). Gently fold the ingredients in until it forms one cohesive batter. Your "batter" may be very dry and powdery, that's fine.
Spread the mixture into your prepared pan, pressing it into all corners and making sure it is level.
Bake for about 30 minutes. Let the brownies cool completely before making the frosting.
Chocolate Fudge Frosting
Beat butter and cocoa powder on a medium speed until smooth. Scrape the bowl down and add the corn syrup. On a medium speed, beat until smooth. Scrape the bowl down.
With the mixer on a med- low speed, slowly pour the boiling water into the bowl. Continue mixing until well combined. Scrape the bowl down.
Add the powdered sugar, vanilla, and salt. Beat on a low speed until mostly combined, then increase to med- high speed and beat for 2 minutes.
Spread onto the cooled brownies and chill in the fridge for one hour to make slicing the brownies super easy.