Shred the zucchini into a liquid measuring cup until you reach 2 cups. Then press down the zucchini as much as it will go and pour out any juice that forms.
Preheat oven to 350 degrees. Spray a 9x13 pan with non-stick cooking spray. Line the bottom with parchment paper and then spray that with cooking spray. Set aside.
In a large mixing bowl, add in the vegetable oil, granulated sugar and brown sugar. Mix with a hand mixer for 2 minutes on high.
Add in the vanilla extract and egg. Beat until incorporated.
Add in the shredded zucchini and stir until combined.
In a separate bowl, sift together the cocoa powder, flour and baking soda. Then dump the dry ingredients into the wet ingredients. Stir to combine.
Pour the brownie batter into the prepared 9x13 pan.
Place into the preheated oven and bake for 38 minutes. Remove from the oven and let cool completely.
Frosting
In a large mixing bowl, add in the butter, cocoa powder and chocolat extract. Mix with a hand mixer until incorporated.
Add in the milk and powdered sugar and beat on low. Once the powdered sugar is mostly incorporated, turn mixer on high and let it beat for an additional 2 minutes until light and fluffy.
Spread the chocolate frosting onto the cooled brownies. Cut and serve.
Notes
To cut my brownies, I refrigerated my brownies with the frosting overnight.