1In large bowl, mix beef, mushrooms, cornstarch, garlic and teriyaki sauce. Let stand at room temperature 15 minutes, stirring occasionally. Drain beef and mushrooms well, reserving marinade. Cook frozen broccoli as directed on bag.
2In 12-inch skillet, heat oil over medium-high heat. Cook beef, mushrooms and green onions in oil 3 to 5 minutes, stirring frequently, until beef is no longer pink. Stir in cooked broccoli.
3Gradually add reserved marinade. Cook over medium-high heat 2 to 3 minutes, stirring constantly, until mixture thickens. Serve over rice.