In a small bowl, combine cornstarch and water until smooth. Stir in pie filling. Pour into crust.
For topping, combine flour, oats and sugars in another small bowl; cut in the butter until crumbly. Sprinkle over filling. Bake at 375° for 35-40 minutes or until filling is bubbly and topping is browned. Cool on a wire rack; refrigerate until chilled.