In a bowl, combine the sliced beef with 1 tablespoon soy sauce, 1 teaspoon cornstarch, and 1 teaspoon sesame oil. Mix well and let it marinate for at least 15 minutes.
2. Prepare the Sauce:
In a small bowl, whisk together 2 tablespoons soy sauce, oyster sauce, sugar, 1 teaspoon sesame oil, and ground black pepper. Set aside.
3. Cook the Noodles:
Cook the lo mein noodles according to the package instructions. If using spaghetti, cook until al dente. Drain and set aside.
4. Stir-Fry the Beef:
Heat 1 tablespoon of vegetable oil in a large pan or wok over high heat. Add the marinated beef and stir-fry until it’s no longer pink, about 2-3 minutes. Remove the beef from the pan and set aside.