Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom and side of 9- or 8-inch round or square cake pan with baking spray with flour.
In large bowl, beat cake mix, zucchini, cinnamon, cloves, buttermilk, oil and egg with electric mixer on low speed until moistened, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan. Sprinkle evenly with nuts and chocolate chips.
Bake 9-inch pan 27 to 35 minutes, 8-inch pan 32 to 40 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.