Preheat oven to 350. In a 2-quart casserole dish, firmly press hash brown potatoes evenly across bottom to form a shell; set aside. In a large saucepan, combine turkey, onions, and bell peppers. Stir in water, gravy mix, and salt; bring to a boil. Add mixed vegetables; reduce and cook, uncovered, five minutes. Remove from heat. Stir in half cup cheddar cheese. Spoon in hash brown potato shell. Bake, uncovered, for 15 minutes or until heated through. Top with remaining cheddar cheese. Bake, uncovered again, for five minutes more.