Cut the flank steak lengthwise into strips 1 ½ inches wide, then crosswise into ¼ in. slices. Clean vegetables and cut into appropriate sizes.
In a large bowl, mix the soy sauce, sugar, cornstarch, chopped onion, and the steak slices. The steak should be marinated for at least one hour. Just before frying the steak, add 1 t. oil to it and mix well. Heat the pan for 30 seconds and then heat the oil for another 30 seconds. Fry beef and stir briskly over high heat for 1 minute, or until the meat shows no sign of pink. Drain and remove from pan. In the same pan, stir fry the vegetables for about 1 minute. Add the salt. Add beef, blend thoroughly and stir for ½ minute. Serve.
Beef with broccoli: 1 lb. Flank steak with ½ bunch broccoli
Beef with green beans: ½ lb. Flank steak with 1 lb. Green beans
Beef with fresh mushrooms: 1 lb. Flank steak with 6-8 oz. Fresh mushrooms
Beef with pea pods: 1 lb. Flank steak with ¼ lb. Pea pods
Beef with green peppers: 1 lb. flank steak with 2 cut-up peppers