Preheat oven to 350°. In a large bowl, beat the sugar, oil, eggs and vanilla until well blended. Combine the flour, baking powder, salt, cinnamon and baking soda; gradually beat into sugar mixture until blended. Fold in apples and walnuts., Transfer to a greased 13x9-in. baking dish. Bake until a toothpick inserted in the center comes out clean, 35-45 minutes. Cool on a wire rack. Serve with whipped topping.