Sauté onion and pepper in 2 tablespoons of butter until soft, about five minutes. Add basil and tomatoes including juice. Cook on high heat, stirring until most liquid has evaporated. Stir in turkey, salt and pepper. Pour in casserole. Mix cream cheese with remaining 4 tablespoons butter until well blended. Gradually beat in milk until smooth; spread over ingredients in casserole. Sprinkle with cheeses. Bake uncovered at 400° for 20 minutes or until bubbly.