In bowl, add chicken, Shaoxing wine, soy sauce, cornstarch and salt, tossing to coat. Let marinate 10 to 15 minutes.
Place chow mein in a large bowl; cover with hot tap water and let stand 1 minute. Drain and set aside.
In a 2-cup measure, stir together oyster sauce, soy sauce, sesame oil, sugar, pepper and salt; stir in chicken stock. In small bowl, stir together 1 tbsp cornstarch and 2 tbsp cold water.
Heat 2½ tbsp of the vegetable oil in extra-large skillet over high heat until hazy. Spread noodles in an even flat circle and fry until brown and crispy, 4 to 5 minutes. Flip using large spatula and continue cooking 2 to 3 minutes. Slide onto platter.
Heat remaining 1 tbsp oil over high heat until hazy. Add chicken, spreading out evenly, and cook, stirring, until browned, 2 to 3 minutes; add garlic and white parts of green onions, stirring for 30 seconds. Add chicken stock mixture and bring to a boil.
Stir in choy sum, then cornstarch mixture and cook, stirring; bring to a boil. Stir in green onions and immediately pour over crispy noodles.
Serve with chili crisp or hot sauce.