Start by slicing the boneless, skinless chicken into bite-sized pieces. In a bowl, combine the chicken with soy sauce, cornstarch, and sesame oil, mixing well. Let it marinate for about 5-10 minutes while you prepare the other ingredients.

Bring a large pot of salted water to a boil and cook the lo mein noodles according to the package instructions, typically 3-5 minutes. Once cooked, drain the noodles in a colander and toss them with a drizzle of sesame oil to prevent sticking. Set them aside.

In a medium bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, brown sugar, chicken broth (or water), and toasted sesame oil. Ensure everything is well combined.

Heat a wok or large skillet over medium-high heat, then add vegetable oil. Once the oil shimmers, add the marinated chicken. Sauté for about 5-7 minutes until browned and cooked through. Remove from the pan and set aside.

In the same pan, add minced garlic (and fresh ginger, if desired) and sauté for roughly 30 seconds until fragrant. Then, add the sliced bell peppers, shredded carrots, and snap peas. Stir-fry for 3-4 minutes until crisp-tender.

Return the cooked chicken to the pan with sautéed vegetables, then pour in the prepared sauce. Stir everything together and let it simmer for about 1-2 minutes. Finally, toss in the cooked noodles and sliced green onions, mixing gently until heated through, and serve hot.