To make the crust, combine 1 cup of flour and 2 teaspoons of sugar in a large bowl or food processor. Add 3 tablespoons of chilled margarine and process (or mix together with your fingers if you do not have a food processor) until mixture resembles coarse meal. Add cold water, one tablespoon at a time, and process or mix until a manageable dough forms. Press dough into the bottom and up the sides of a 9-inch pie plate. Pinch the edges to form a decorative rim; set aside.
2To make the filling, combine apples, 1/4 cup of sugar, cornstarch and cinnamon in a large bowl; toss to coat apples. Arrange mixture in prepared piecrust.
3To make the topping, combine oats, 5 tablespoons of flour, 2 tablespoons of sugar and melted margarine in a small bowl; sprinkle over apples.
4Bake until apples are tender and crumb topping is golden brown, about 45 to 50 minutes. Allow to cool for 30 minutes before slicing into 8 pieces.