Prepare all ingredients: slice chicken, chop vegetables, mince garlic and ginger, and cook lo mein noodles according to package instructions.
In a large skillet or wok, heat vegetable oil over medium-high heat. Add sliced chicken and cook for 5-7 minutes until browned and cooked through. Remove from skillet and set aside.
In the same skillet, add mixed vegetables, minced garlic, and ginger. Stir-fry for 3-4 minutes until tender-crisp.
Return cooked chicken to the skillet, add cooked lo mein noodles, soy sauce, oyster sauce, sesame oil, sugar, and black pepper. Toss everything together and cook for an additional 2-3 minutes until heated through.
Serve hot, garnished with chopped green onions.