Feel free to improvise with this stir-fry. Try sliced pork or chicken instead of the beef. Use green, yellow or orange bell pepper instead of the red pepper and either
crookneck squash or yellow summer squash instead of the green zucchini. How colorful!
Flank steak is a less-tender, inexpensive cut of beef. The sauce ingredients, which are acidic, tenderize the beef in addition to adding great flavor.