In small skillet, stir-fry steak in oil for 4 minutes or until no longer pink. Remove steak and keep warm. Stir-fry green pepper and celery until crisp-tender. Combine cornstarch, water, soy sauce, sugar and salt until smooth; add to skillet.
Bring to boil. Cook and stir for 1 minute or until thickened. Add steak and tomato to skillet; heat through. Serve over rice. Makes 1 serving.