Make spaghetti according to package directions. Brown ground beef in skillet, then add spaghetti sauce and warm it through. In a glass, microwave-safe dish, combine green pepper, onions and butter. Microwave on high for 4 min. until veggies are soft. Add cream cheese and milk to the vegetables. Assemble casserole: In a 2 L casserole dish, pour a small amount of a sauce to cover the bottom. Top with drained spaghetti. Top with cream cheese vegetables, and top that with remainder of spaghetti sauce. Sprinkle cheeses over top. Bake uncovered at 350°F for 25 minutes. Let stand few minutes before serving.