I found this recipe originally here; I added some milk, but otherwise the recipe is as is.
1/2 cup vegetable oil
1 1/2 cups white sugar
2 teaspoons vanilla extract
2 cups all-purpose flour
1/2 cup unsweetened cocoa powder
1 1/2 teaspoons baking soda
1 teaspoon salt
2 cups shredded zucchini
1/2 cup milk
1/2 cup chopped walnuts
6 tablespoons unsweetened cocoa powder
1/4 cup margarine
2 cups confectioners' sugar
1/4 cup milk
1/2 teaspoon vanilla extract
Preheat oven to 350. Grease and flour a 9x13 inch baking pan.
Combine the flour, 1/2 cup cocoa, baking soda and salt. Set aside.
In a standing mixer combine oil, sugar, 2 teaspoons vanilla and milk until well blended. Add flour and cocoa, then fold in the zucchini and walnuts. Pour into pan.
Bake for 25 to 30 minutes at 350 degrees. Then set aside to cool.
To make icing, melt together the 6 tablespoons of cocoa and margarine; set aside to cool. In a medium bowl, blend together the confectioners' sugar, milk and 1/2 teaspoon vanilla. Stir in the cocoa mixture. Spread over cooled brownies before cutting into squares.