1Preheat oven to 350 degrees. Spray a 9 x 13-inch pan with nonstick baking spray.
2Mix together flour, baking powder, baking soda, and spices.
3In a large bowl, with an electric mixer, cream the margarine and prunes together. Add pumpkin puree, Splenda, molasses, vanilla, and egg. Beat well. Stir in flour mixture. Stir in raisins. Spoon into prepared pan and smooth. Bake for 20 minutes, or until cake springs back when lightly touched in the center. Cool on rack.
4In a small bowl, with an electric mixer, beat all frosting ingredients until smooth and fluffy. Spread frosting onto cool bars. Refrigerate. Twenty-four servings.