Bring a pot of water to a boil and cook the noodles to the lower end of the package instructions so they stay slightly underdone. Drain and set aside.
Meanwhile, slice the chicken breast into thin, bite-sized pieces.
Add the chicken to a bowl with light soy sauce, chicken bouillon, sesame oil, and Shaoxing wine. Mix until evenly coated.
Combine the light soy sauce, oyster sauce, sugar, chicken bouillon, and a splash of water for the sauce. Mix until everything is dissolved and set aside.
Heat oil in a wok or pan over high heat.
Add the chicken and sear or stir-fry until lightly browned and just cooked through. Remove and set aside.
Add a bit more oil if needed, then add the garlic and ginger and bloom for a few seconds until fragrant.
Add the Chinese broccoli, squash, bell pepper, and onion. Stir-fry until lightly softened, working in batches if needed to avoid overcrowding the pan.
Add the noodles and sauce. Toss until glossy and evenly coated.
Return the chicken to the pan and mix to combine.
Add the bean sprouts at the end to keep them fresh and crisp.
Notes
The noodles are reduced and the chicken and vegetables increased compared with takeout-style lo mein for a higher-protein version.
Slightly undercook the noodles before stir-frying so they finish in the sauce without becoming soggy.