Preheat the oven to 375 degrees. Prepare a deep dish pie plate with nonstick cooking spray.
Place the potatoes in a small, microwave-safe bowl with the water. Cover with plastic wrap, vented on one side. Microwave on high for 4 to 5 minutes, depending on the wattage of your microwave, or until the potatoes are beginning to soften. Drain well.
Meanwhile, in a medium saucepan over medium heat, melt the butter. Stir in the seasonings and flour and cook for 2 minutes. Slowly add the milk, stirring constantly. Continue cooking until the sauce has thickened slightly. Stir in the cheese and remove from heat.
Place one pie crust into the bottom of the pie plate. On the pie crust, place the potatoes, onions, bacon, and green beans. Pour the cheese sauce over the top. Cover the pie with the remaining pie crust, pressing to seal the edges. Cut small holes in the top to vent.
Bake for 50 to 60 minutes until the crust is golden. Allow the pie to rest for 10 minutes prior to cutting.