In a large, skillet over medium heat, cook the sausage, onion, celery and mushrooms in oil until meat is no longer pink; drain if necessary. In a large bowl, combine the remaining ingredients; add sausage mixture and toss to coat.
Transfer to a greased 11-by-7-by-2 inch baking dish. Cover and bake at 350 degrees for 30 minutes. Uncover; bake 10-15 minutes longer or until lightly browned.