Combine sugar and cornstarch in saucepan; stir in orange rind and juice. Bring to a boil, cook, stirring constantly, for 1 minute. Remove from heat. Add rhubarb and strawberries; stir gently. Spoon into pastry shell.
TOPPING: Combine flour, brown sugar and quick cooking oats in a bowl and then cut in 2 tablespoons margarine with a pastry blender until mixture resembles coarse meal. Sprinkle over rhubarb mixture.