In a bowl, combine the soy sauce, garlic and ginger. Add beef; toss to coat. Let stand for 15 minutes. In a large skillet, stir-fry beef mixture in oil for 2 minutes. Add celery and red pepper; stir-fry for 2 minutes. Add onions and mushrooms; cook 2 minutes longer.
Drain pineapple, reserving juice. Stir pineapple and water chestnuts into skillet. In a bowl, combine cornstarch, water and reserved pineapple juice until smooth. Gradually stir into beef and vegetables. Bring to a boil; cook and stir for 1-2 minutes or until thickened. Serve over rice.