Cook lo mein noodles according to package directions and drain.
Toss sliced beef with cornstarch and set aside.
Heat 1 tablespoon oil in a large wok or skillet over high heat.
Cook beef for 2–3 minutes until browned and remove from pan.
Add remaining oil, then sauté garlic and ginger for 30 seconds.
Add broccoli and bell pepper and stir-fry for 3–4 minutes.
Return beef to the pan.
Stir in soy sauce, oyster sauce, hoisin sauce, sesame oil, and water.
Add cooked noodles and toss everything together until well coated.
Cook for 2–3 more minutes until heated through.
Garnish with sliced green onions and serve immediately.