Cream together sugar, margarine and eggs. Add salt, flour, oatmeal, cinnamon and baking powder. Add soda and water last. Drop on pans. Bake 350 for 10 minutes. Filling: Beat egg whites till stiff. Add vanilla, flour and milk. Beat well and add oil and sugar. The more you beat the fluffier it gets. When cookie part cools spread filling on two and put together.