In a large skillet, cook beef, onion and garlic over medium heat until meat is no longer pink; crumble beef; drain. Add bean sprouts, mushrooms and water chestnuts. Cook and stir for 3-5 minutes. Stir in the vermicelli, broccoli, soy sauce, oyster sauce if desired and ginger; toss to coat. Cover and cook for 5 minutes or until heated through.