Preheat the oven to 325 degrees F.
Cream the butter, then add the oil and sugar; mix.
Add the zucchini, eggs, buttermilk, vanilla, cocoa, flour, baking soda and salt; mix well.
Fold in the chocolate chips and walnuts by hand.
Place the cake in a greased and floured 9×13 pan.
Bake for about 1 hour (or until