In a large bowl, combine the oil, sugars, eggs and vanilla; mix well. Combine the flour, baking soda, salt and cinnamon; add to the egg mixture alternately with buttermilk. Stir just until moistened. Stir in coconut and walnuts just until combined.
Pour into a greased 13-in. x 9-in. baking pan. Bake at 350° for 45-55 minutes or until toothpick inserted near the center comes out clean. Cool on a wire rack. Dust with confectioners' sugar if desired. Yield: 12-15 servings.