Heat oven to 325°F. Cook spaghetti to desired doneness as directed on package. Drain; rinse with hot water.
Meanwhile, in large skillet, cook bacon over medium heat until crisp. Drain bacon on paper towels; set aside. Drain all but 1 tablespoon bacon drippings from skillet.
Stir in onion and bell pepper; cook until crisp-tender. Add cooked spaghetti, bacon, tomatoes and 1 1/2 cups of the cheese; mix well. Place in ungreased 2-quart casserole.
Bake at 325°F. for 45 to 60 minutes or until hot and bubbly. Top with remaining 1/2 cup cheese. Bake an additional 5 minutes or until cheese is melted.