Trim fat from beef; discard. Slice beef across prominent grain into 1/4 inch thick slices. Rinse zucchini; cut off ends. Cut each zucchini crosswise and lengthwise in half. Cut pieces lengthwise into 1/2 inch strips. Cut onion lengthwise in half and slice crosswise into 1/4 inch slices. Heat wok over high heat about 1 minute or until hot. Add sesame seeds and cook until lightly browned. Remove to a small bowl. Drizzle 1 tablespoon oil into the wok and heat for 30 seconds. Add beef and stir fry about 2 minutes or until well browned on outside and rare on the inside. Remove beef to a large bowl. Reduce heat to medium Add remaining 1 tablespoon of oil to the wok. Add mushrooms, zucchini and onion; stir fry about 5 minutes or until vegetables are crisp tender. Stir in teriyaki, sugar salt and pepper. Return beef and any accumulated juices to the wok, heat through. Spoon hot cooked rice onto a serving plate; top with the beef mixture. Sprinkle with sesame seeds.