Preheat oven to 350 degrees F. Grease and flour a 9 x 13 inch baking pan.
In a large bowl, mix together the oil, sugar and vanilla.
Combine the flour, 1/2 cup cocoa, baking soda and salt. Stir into the sugar mixture. Fold in the zucchini and walnuts. Spread evenly in to the prepared pan.
Bake 25 - 30 minutes in the preheated oven, until brownies spring back when gently touched.
Frosting
Melt together 6 tbsp cocoa and butter (or margarine, but I always suggest butter)
Blend together the confectioners’ sugar, milk and 1/2 tsp vanilla. Stir in the cocoa mixture. Spread over cooled brownies before cutting into squares.