In a bowl, combine the thinly sliced beef with soy sauce, cornstarch, and sesame oil. Mix well and let it marinate for at least 15 minutes.

If using dried rice noodles, soak them in warm water until they are soft, then drain. If using fresh noodles, separate them gently with your hands. Set aside.

Heat 1 tablespoon of vegetable oil in a wok or large frying pan over high heat. Add the marinated beef slices and stir-fry until they are just cooked through. Remove the beef from the wok and set aside.

In the same wok, add another tablespoon of vegetable oil. Add the minced garlic and scallions, stir-frying for a few seconds until fragrant.

Add the rice noodles to the wok, tossing and stirring to prevent them from sticking. If the noodles start to stick, a splash of water can help loosen them.

Add the soy sauce, dark soy sauce, and oyster sauce to the noodles. Continue to stir and toss the noodles until they are evenly coated with the sauce.

Return the cooked beef to the wok, along with the bean sprouts. Toss everything together for another 1-2 minutes, ensuring the ingredients are well mixed and heated through.

Drizzle a dash of sesame oil over the dish and give it one final stir. Serve hot, garnished with additional scallions if desired.