What's for Dessert? Zucchini Chocolate Cake with Walnuts

Matt brought home a huge zucchini from work yesterday, and I needed to use it up quickly. I am running low on a lot of things (like regular flour and butter), so I came up with this, using what I did have.

cinnamon-sugar, divided
1/2 cup vegetable oil
1 cup sugar
3 eggs
1/2 cup buttermilk
2 t vanilla
1 cup flour
1 cup whole wheat flour
1/4 cup cocoa powder
1 t baking soda
1/2 t baking powder
1 t cinnamon
2 cups grated zucchini
1 cup walnuts

Preheat oven to 350°. Spray a 13x9" baking pan with cooking spray. Sprinkle with cinnamon-sugar, just to cover bottom of pan. Set aside.

In a large bowl, mix oil and sugar til smooth. Add eggs, one at a time, beating well after each addition. Stir in buttermilk and vanilla. Set aside.

In a medium bowl, sift together flours, baking powder, baking soda and cinnamon. Add dry ingredients to wet mixture; alternate with grated zucchini. Pour into prepared pan. Top with cinnamon-sugar (I used about 1 T) and sprinkle with walnuts.

Bake for 30-35 minutes or til a toothpick inserted in the center comes out clean.