Marinate the Beef:

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

Prepare the Noodles:

If the rice noodles are refrigerated or stiff, blanch them in boiling water quickly or follow the package instructions to loosen them up. Be careful not to overcook. Drain and set aside.

Cook the Beef:

Heat half of the vegetable oil in a wok or large skillet over high heat. Add the marinated beef and stir-fry until just browned. Remove the beef from the wok and set aside.

Stir-Fry the Noodles:

Add the remaining oil to the wok. Sauté the garlic and onions until fragrant. Add the rice noodles and stir-fry, ensuring they don't stick to the wok. If the noodles start to stick, a splash of water can help loosen them.

Combine Ingredients:

Return the beef to the wok along with the bean sprouts and green onions. Add the dark soy sauce and light soy sauce, and season with salt and pepper. Stir-fry everything together until well combined and the bean sprouts are just tender.

Serve:

Remove the wok from the heat. Taste and adjust the seasoning if necessary. Serve hot.