Slice the boneless, skinless chicken breast into thin strips. Heat vegetable oil in a large skillet or wok over medium-high heat. Add the sliced chicken and cook for 5-7 minutes until no longer pink. Remove and set aside.
Cook the egg noodles according to package instructions, about 5-7 minutes. Drain and set aside.
In the same skillet, add mixed vegetables, minced garlic, and minced ginger. Stir-fry for 3-4 minutes until tender-crisp.
Return the cooked chicken to the skillet. Whisk together soy sauce, oyster sauce, sesame oil, sugar, and black pepper in a bowl. Pour over chicken and vegetables, stirring to combine.
Add the cooked egg noodles to the skillet. Toss gently until heated through and well coated with sauce. Garnish with sliced green onions before serving.