Combine all ingredients except spaghetti and cheese in 4-quart (or larger) slow cooker.
Cover. Cook on Low 6–8 hours, or on High 3–5 hours. Turn to High during last 30 minutes and stir in dry spaghetti. (If spaghetti is not fully cooked, continue cooking another 10 minutes, checking to make sure it is not becoming overcooked.)