Preheat oven to 350°. Cook spaghetti according to package directions for al dente., In a large skillet, cook bacon and onion over medium heat until bacon is crisp, stirring occasionally; drain. Stir in tomatoes and tomato sauce; bring to a boil., Drain spaghetti; transfer to a greased 11x7-in. baking dish. Spread sauce over top. Bake, covered, 40-45 minutes or until bubbly. If desired, sprinkle with parsley.