In a large skillet, heat oil over medium heat; add ground beef, celery, and chopped onion.
Fry until beef is browned and onions are tender. Remove from heat and put into large casserole. Add the tomatoes, the cooked macaroni, shredded cheese, sauce, salt and pepper.
Bake at 350° for 30 minutes, until hot and bubbly.
Sprinkle beefy macaroni casserole with chopped parsley, if desired.