In a large bowl, cream shortening and brown sugar until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Beat in pumpkin and vanilla. Combine the flour, cinnamon, baking powder, baking soda, ginger and nutmeg; add to creamed mixture and mix well. Stir in nuts., Spread into a greased 13x9-in. baking dish. Bake at 350° for 20-25 minutes or until a toothpick inserted in the center comes out clean. Cool on a wire rack., In a large bowl, beat the shortening, confectioners' sugar, orange juice and zest until blended. Frost bars; cut into squares. If desired, top with candy pumpkins or decorate with colored frosting.