Cook the spaghetti according to package directions. Meanwhile, in a large nonstick skillet over medium heat, cook the sausage in oil for 5 minutes. Add onion; cook 8-10 minutes longer or until meat is no longer pink and onion is tender.
Stir in the tomatoes and basil; heat through. Add the cream; bring to a boil. Drain spaghetti; toss with sausage mixture. Garnish with cheese if desired.