In a bowl, combine flour, sugar, cinnamon, baking soda and salt. In a separate bowl, mix oil, eggs and vanilla; add to flour mixture and beat. Add zucchini; mix well. Fold in nuts. Pour into three well-greased 9-in. round baking pans. , Bake at 325° for 30-40 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely. , For frosting, beat cream cheese and butter; blend in sugar and vanilla. Beat until smooth. Frost between layers and top and sides of cake.