In a bowl, combine the sliced flank steak, soy sauce, and cornstarch. Mix well and let it marinate for at least 15 minutes.

Cook the rice noodles according to package instructions. Drain and set aside.

Heat vegetable oil in a wok over high heat. Add the marinated beef and stir-fry until browned, about 3-4 minutes.

Add the bell pepper, broccoli, and carrots. Stir-fry for another 3-4 minutes until the vegetables are tender-crisp.

In a small bowl, mix hoisin sauce, oyster sauce, sesame oil, sugar, garlic, and ginger. Pour the sauce over the beef and vegetables.

Add the cooked noodles to the wok and toss everything together until well coated in the sauce. Cook for an additional 2 minutes.

Serve hot, garnished with sliced scallions.