Spray a 22 cm (8-inch) square baking dish with vegetable cooking spray. Set aside
Whisk together 1 cup Splenda Granular Sweetener, 1 tsp cinnamon, grated orange zest and orange juice in a large bowl; add peeled, cored and sliced apples and toss to coat
Stir together oats, 2 tbs Splenda Granular Sweetener, and 1/4 tbs cinnamon in a medium bowl; cut margarine in with a pastry blender or 2 knives until mixture is crumbly
Stir in cereal and chopped walnuts
Transfer apple mixture to prepared pan; spoon cereal topping over apples
Bake for 45 minutes or until topping is lightly browned. Serve warm