Cook the egg noodles according to package instructions. Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat.
Add the sliced chicken breast to the skillet and season with salt and pepper. Cook until the chicken is browned and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.
In the same skillet, add the mixed vegetables, green onions, garlic, and ginger. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.
Return the cooked chicken to the skillet with the vegetables.
In a small bowl, mix together the soy sauce, oyster sauce, sesame oil, and sugar. Pour the sauce over the chicken and vegetables, stirring to combine.
Add the cooked egg noodles to the skillet and toss everything together until well combined and heated through, about 2-3 minutes.
Serve hot, garnished with additional green onions if desired.