Bring a large pot of salted water to a boil. Add the lo mein noodles and cook according to the package instructions (usually about 3-5 minutes). Drain and set aside.
In a small bowl, whisk together the soy sauce, oyster sauce, sesame oil, cornstarch, garlic powder, and ground ginger until smooth.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the sliced chicken and stir-fry for about 5-7 minutes, or until cooked through.
In the same skillet, add the remaining tablespoon of oil. Add the bell peppers, broccoli, carrots, and snap peas. Stir-fry for about 4-5 minutes until the vegetables are tender-crisp.
Return the cooked chicken to the skillet with the vegetables. Pour the prepared sauce over and stir well to coat everything.
Add the cooked lo mein noodles to the skillet. Toss until the noodles are heated through and well coated with the sauce.
Remove from heat, garnish with chopped green onions, and serve immediately.