2 1/4 cups sifted all purpose flour
1/2 cup unsweetened cocoa powder
1 teaspoon baking soda
1 teaspoon salt
1 3/4 cups sugar
1/2 cup (1 stick) unsalted butter, room temperature
1/2 cup vegetable oil
2 large eggs
1 teaspoon vanilla extract
1/2 cup buttermilk
2 cups grated unpeeled zucchini (about 2 1/2 medium)
1 6-ounce package (about 1 cup) semisweet chocolate chips
3/4 cup chopped walnuts
Preheat oven to 325°F. Butter and flour 13 x 9 x 2-inch baking pan. Sift flour, cocoa powder, baking soda and salt into medium bowl. Beat sugar, butter and oil in large bowl until well blended. Add eggs 1 at a time, beating well after each addition. Beat in vanilla extract. Mix in dry ingredients alternately with buttermilk in 3 additions each. Mix in grated zucchini. Pour batter into prepared pan. Sprinkle chocolate chips and nuts over.
Bake cake until tester inserted into center comes out clean, about 50 minutes. Cool cake completely in pan.