Trim fat from meat. Partially freeze the meat. With a very sharp knife, cut beef across the grain into thin, bite-size strips. In a medium bowl, combine soy sauce, garlic, and ginger. Add beef strips; toss to coat. Set aside while preparing the vegetables.
In a large skillet or wok, heat 1 tablespoon oil. Add green onions, green pepper, and celery; stir-fry over high heat until crisp-tender. Remove from the skillet or the wok.
Drain beef, reserving soy sauce mixture. Add more oil to skillet, if necessary. Stir-fry half of beef for 2 to 3 minutes or until thoroughly cooked. Remove from skillet or wok. Repeat with remaining beef. Return all beef to skillet.
In a small bowl, stir together reserved soy sauce mixture, water, and cornstarch. Add mixture to the beef in the skillet. Cook and stir until mixture is thickened and bubbly. Add the cooked vegetables and tomatoes; heat through. Serve with rice or noodles. Makes 4 servings.