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 milk or 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 (optional)