Preheat oven to 350. In a 2 litre casserole dish , firmly press hash brown potatoes evenly across bottom to form a shell; set aside. Meanwhile, in a skillet, heat oil over medium heat. Add turkey, onions, and bell peppers. Cook until turkey is longer pink and vegetables are tender. Stir in water, gravy mix, and salt; bring to a boil. Add mixed vegetables; reduce and cook, uncovered, 5 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 5 minutes more.