Heat oven to 325. Cook spaghetti according to desired doneness as directed on package. Drain; rinse with hot water. Place in ungreased 2-quart casserole.
In large skillet, fry bacon until crisp. Drain on paper towels. Drain all but 1 tablespoon bacon drippings from skillet. Stir in onion and green pepper; cook until crisp-tender. Stir into spaghetti Add bacon, tomatoes, and 1 1/2 cups cheese; mix well. Bake for 45-60 minutes or until hot and bubbly Top with remaining 1/2 cup cheese; bake 5 minutes or until cheese is melted.