Prepare the lo mein noodles according to package instructions. Drain and set aside.
In a bowl, combine the sliced beef with soy sauce, oyster sauce, sesame oil, garlic, and ginger. Let it marinate for about 10 minutes while you prepare the vegetables.
Heat a large skillet or wok over medium-high heat. Add a splash of sesame oil and stir-fry the marinated beef for about 2-3 minutes until browned and just cooked through. Remove from the skillet and set aside.
In the same skillet, add a little more sesame oil if needed. Stir-fry the bell peppers and snap peas for 2-3 minutes until tender-crisp.
Return the beef to the skillet with the cooked vegetables. Add the cooked lo mein noodles and toss everything together, ensuring the noodles are well coated in the sauces.
Season with salt and pepper to taste and adjust any sauces as desired. Toss in chopped green onions just before serving.
Notes
Serve in large bowls garnished with additional green onions and sesame seeds for an appealing finish.