In a bowl, combine flour, sugar, baking powder, baking soda, cinnamon and salt. Stir in eggs, squash and oil; mix well. Spread into a greased 15x10x1-in. baking pan. Bake at 350° for 25-30 minutes or until a toothpick comes out clean. Cool on a wire rack. , Meanwhile, for frosting, beat together cream cheese, confectioners' sugar, vanilla and butter. Add milk; stir until smooth. Frost cooled cake. Cut into squares.