Cut steak into 2-in x 1/8-in strips. In a large skillet or wok, brown steak in oil. Add garlic, ginger, salt if desired and pepper; cook 1 minute. Remove meat and keep warm. Add green peppers and onions to skillet; cook and stir for 5 minutes or until crisp-tender. Dissolve bouillon in hot water; add to skillet with water chestnuts. Combine cornstarch, soy sauce, cold water and sugar; stir into skillet. Add meat. Cook and stir until mixture boils; cook and stir 2 minutes more.