Preheat the oven to 350 degrees F. Spray a deep-dish pie pan with nonstick spray and set aside.
To make the crust: Place cereal and graham cracker pieces in a blender or food processor, and grind to a breadcrumb-like consistency. Transfer to a medium bowl. Add white sugar and cinnamon, mix well, and set aside.
In a small microwave-safe bowl, combine butter with 2 tablespoons water. Microwave for 15 seconds, or until just melted. Add to the medium bowl and stir contents until thoroughly mixed. Evenly distribute crust mixture along the bottom of the pie pan. Using your hands or a flat utensil, firmly press mixture into the edges and up along the sides of the pan to form the crust.
Bake crust in the oven for 10 minutes. Set aside to cool.
Set oven to 375 degrees F. Peel, core, and thinly slice 8 cups worth of apples. Set aside.
In a large nonstick pot on the stove, combine all ingredients for the filling except apples and optional topping. Add 1 1/2 cups cold water and mix until ingredients have dissolved. Add apples and stir. Bring to medium-high heat and, stirring frequently, cook until liquid has thickened and apples have softened, 12 to 15 minutes.
Carefully transfer filling to the crust in the pan, and smooth out the surface with the back of a spoon. Bake in the oven until apples are very tender, 20 to 25 minutes.
Allow pie to cool and set completely. Cut into 8 slices and, if you like, top each serving with a generous squirt of whipped topping. Enjoy!
PER SERVING (1/8th of pie, 1 slice): 159 calories, 3g fat, 167mg sodium, 37g carbs, 5.5g fiber, 23g sugars, 1g protein