Boil chow mein noodles according to package instructions, drain, and rinse with cold water.
Toss sliced beef with soy sauce, oyster sauce, and cornstarch. Let sit for 15 minutes.
Heat 1 tbsp oil in a hot skillet or wok, stir-fry beef until browned, about 2–3 minutes. Remove and set aside.
Add remaining oil. Stir-fry garlic and ginger for 30 seconds until fragrant.
Add bok choy, bell pepper, and carrot. Cook 3–4 minutes until tender-crisp.
Return beef and add noodles. Toss to coat and stir-fry another 2–3 minutes.
Season with salt, pepper, and more soy sauce to taste. Garnish with green onions.
