Preheat oven to 325°F. Spray 8-inch-square baking dish with nonstick cooking spray; set aside. In large bowl, combine water, rolled oats and 1/4 cup plus 2 tablespoons margarine; cool to lukewarm. With electric mixer at medium speed, beat in sugar, 6 packets Sweet One®, 2 tablespoons molasses, egg and vanilla. In small bowl, stir together flour, cinnamon, baking powder, baking soda and salt; stir into oatmeal mixture until well blended.

In large metal bowl with electric mixer at high speed, beat egg whites and cream of tartar until stiff peaks form; fold into batter. Spoon batter into prepared pan. Bake in center of over 25 to 30 minutes or until wooden pick inserted in center comes out clean. Cool on wire rack.

Prepare topping: Preheat oven to broil. In small saucepan over medium heat, cook 2 tablespoons margarine, milk, 1-1/2 teaspoons molasses and 2 packets Sweet One® 2 to 3 minutes or until bubbly and slightly thickened. Stir in Walnuts and coconut, if desired. Spread on cake. Broil 3 to 4 inches from heat source 30 seconds or until nuts begin to brown. Cool on wire rack