Mix cornstarch, sugar and cinnamon in a saucepan. Add 3/4 cup water and mix well. Add apples. Cook over low heat, stirring occasionally, until liquid thickens and apples just begin to soften, about 6 minutes. Pour into 1 quart casserole dish. Stir biscuit mix and margarine together. Add 3 tablespoons water and mix well. Spread on top of apple mixture. Bake at 400°F until top is lightly browned, about 30 minutes. Yield: 6 servings.