Prepare Beef
Trim gristle from beef. Cut into chunks, then slice ⅛-inch thick against the grain.
Mix beef with cornstarch, sugar, water, oil, 1 tbsp light soy sauce, 1 tbsp oyster sauce, and white pepper.
Prepare Vegetables
Cut napa cabbage stems with two angled cuts.
Slice sweet pepper, snow pea, green onion, carrot, and garlic.
Cook Noodles
Boil water. Cook lo mein according to package directions.
Drain noodles and toss with 3 tbsp oil, 0.5 tbsp light soy sauce, and sesame oil.
Stir-fry
Mix stir-fry sauce ingredients: 1.5 tbsp light soy sauce, 2 tbsp oyster sauce, 1 tbsp dark soy sauce, white pepper, cornstarch, water, and sugar.
Heat wok on high. Add marinated beef and cook.
Add vegetables and stir-fry.
Add noodles and stir-fry sauce. Toss to combine.
