For the brownies: In a medium bowl, whisk together flour, cocoa powder, baking soda and salt and set aside. With an electric mixer, beat sugar, oil and vanilla. Add flour mixture and blend. Mixture will be very dry and powdery at this point. Add shredded zucchini and blend briefly on low speed. Allow mixture to stand for 5-10 minutes so the moisture from the zucchini can be absorbed into the batter.
Meanwhile, preheat oven to 350°F (170° C) and grease* 9x13 inch (25x40 cm) pan. Mix brownie batter on low speed just until blended and stir in chocolate chips, if using. Spread batter in prepared pan and bake for 18-20 minutes, until top springs back when gently pressed. Remove pan from oven and allow brownies to cool on a wire rack.
To make the Chocolate Glaze: beat all glaze ingredients with an electric mixture until blended. Distribute glaze over warm brownies and quickly spread evenly. Chill brownies before cutting for best results. Zucchini Brownies stay fresh and moist for several days covered in refrigerator.
Notes
*To make this recipe vegan, use margarine instead of butter.Recipe adapted fromCrazy for Crust.