Preheat oven 350?. Spray 9 x 13 dish with butter flavored cooking spray. In large bowl mix mashed sweet potatoes, margarine, egg substitute, vanilla, cinnamon, sugar, salt and ff half & half. In small bowl, mix brown sugar and pecans. Pour potato mixture into prepared baking dish. Sprinkle top with brown sugar-pecan mixture. Spray top of cassserole with butter flavor cooking spray. Bake for 30 minutes or until heated through.