1In a mixing bowl, combine flour, sugar, baking powder, baking soda, cinnamon and salt. Stir in eggs, pumpkin and oil; mix well. Spread into a greased 15 x 10 x 1 inch baking pan. Bake at 350 degrees for 25 to 30 minutes or until bars test done. Cool on wire rack. Meanwhile, for frosting, beat together cream cheese, confectioners sugar, vanilla and butter. Add milk and stir until smooth. Frost cooled cake, top with chopped walnuts and cut into squares.