Preheat oven to 350F Spray a 9x13 pan with cooking spray.

In a large mixing bowl whisk together the oil, sugar, eggs, buttermilk, vanilla, and cinnamon until smooth.

Toss together the flour, baking soda, baking powder, and salt, and add the bowl. Mix just until completely blended. Fold in the zucchini and the nuts.

Turn the batter into your prepared pan and bake for about 40 minutes, or until a toothpick comes out without wet batter clinging to it (moist crumbs are fine.) Some ovens run hot or cool, so check carefully.

Let the cake cool completely before frosting.

To make the frosting beat the cream cheese and butter together until fluffy. Add the lemon juice and the sugar, one cup at a time, while beating. Scrape down the sides of the bowl as necessary. Add more sugar if the frosting is too thin, and a little more lemon juice or milk if it is too thick.