In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, sesame oil, sugar, and ground black pepper. Set aside.
Prepare the lo mein noodles according to the package instructions. Drain and set aside.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the sliced chicken and cook until no longer pink, about 4-5 minutes. Remove the chicken from the skillet and set aside.
In the same skillet, add the remaining 1 tablespoon of vegetable oil. Add the sliced onion and minced garlic, and sauté for about 2 minutes or until the onion starts to soften.
Add the julienned carrots and sliced bell pepper to the skillet. Cook for another 2-3 minutes, stirring occasionally.
Add the cooked chicken back to the skillet with the vegetables.
Add the cooked noodles, the sauce and water to the skillet. Toss everything together, making sure the sauce evenly coats the noodles and other ingredients.
Remove from heat, and sprinkle with sliced green onions.
Serve immediately, either as a standalone dish or with additional sides if desired.