Cut beef across grain into thin strips 1/8-inch thick.
Combine soy sauce, garlic, ginger, and add beef.
Toss and set aside.
Heat oil in wok or large skillet.
Add beef and toss over high heat until browned. (If meat is not tender, cover and simmer for 30 to 40 minutes-over low heat.)
Add vegetables and toss over high heat until tender crisp.
Mix cornstarch with water and add to meat and vegetables.
Stir and cook until thickened.
Add tomatoes and heat through.
Serve over rice or noodles. Serves 4.
Can add cauliflower, carrots, broccoli, and sugar pea pods to this basic recipe.