Place the chicken stock, oyster sauce, dark soy sauce, low sodium soy sauce, cornstarch, toasted sesame oil, brown sugar, grated ginger, and minced garlic in a medium mixing bowl.
Stir the sauce mixture until the brown sugar dissolves and the cornstarch is fully incorporated.
If preparing a spicy version, add chili garlic sauce, Lao Gan Ma spicy chili crisp, or Thai chili pepper flakes to the sauce mixture.
Place the chicken pieces in a separate bowl.
Add 1 tbsp of the prepared sauce to the chicken.
Toss until the chicken is lightly coated.
Allow the chicken to marinate briefly while preparing the vegetables and noodles.
Bring a pot of water to a boil.
Cook the noodles until al dente, approximately 1 to 2 minutes less than the package instructions.
Drain the noodles.
Rinse the noodles under cold water to stop the cooking process.
Drizzle the noodles with a very small amount of oil and toss gently to prevent sticking.
If using pre-cooked fresh yellow egg noodles, rinse them under hot water until the strands separate, then drain well.
Heat a wok or large skillet over medium-high heat.
Add the vegetable oil.
Add the marinated chicken pieces to the hot pan.
Cook the chicken until fully cooked through, stirring as needed.
Remove the cooked chicken from the pan and set it aside.
Add the sliced stir fry vegetables to the same pan.
Stir fry the vegetables for 2 to 3 minutes, or until tender but still crisp.
Add the prepared noodles to the pan with the vegetables.
Pour the remaining sauce over the noodles and vegetables.
Toss continuously for 1 to 2 minutes, or until the sauce becomes glossy, slightly thickened, and evenly coats the noodles.
Return the cooked chicken to the pan.
Toss until the chicken, noodles, vegetables, and sauce are fully combined and heated through.
Remove the pan from the heat.
Garnish with chopped scallion and toasted white sesame seeds.
Serve immediately while warm.