Heat oven to 350°F. Grease 13x9-inch pan with shortening or cooking spray; lightly flour. In large bowl, beat sugar, butter, oil, vanilla and eggs with spoon until well blended.
Stir in flour, cocoa, baking soda and buttermilk until well combined. Fold in zucchini, chocolate chips and, if desired, nuts. Spread batter evenly in pan.
Bake 35 to 45 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour. If desired, frost cooled cake.