In a small bowl, add the light soy sauce, dark soy sauce, oyster sauce, sugar, msg if using, and chicken stock. Mix until combined.
Bring a large pot of water to a boil over high heat. Blanch the fresh chow mein noodles for 10 seconds, then drain and rinse off excess starch. Pat dry any excess moisture from the noodles with paper towels. If you are using pre-cooked fresh noodles, you can skip this step.
Heat a wok or large pan over high heat. Add 2 tablespoons of oil and add the scallion whites and onions. Sauté for 1 minute until the vegetables are slightly charred.
Add the chow mein noodles and work quickly to stir fry and separate the noodles and combine them with the onions and scallions. Add the remaining 2 tablespoons of oil to the noodles. Continue stir frying over high heat, mixing and tossing for 2-3 minutes until the noodles begin to char in places.
Add the premixed stir-fry sauce and toss the noodles to combine. Continue stir frying for 3-4 minutes until the sauce has fully absorbed into the noodles. Toss in the scallion greens and bean sprouts and stir fry for another minute. Plate and enjoy!
