Prepare your fresh ingredients: chop bell peppers, julienne carrots, and slice green onions. Cook the lo mein noodles according to the package instructions until al dente, about 3–4 minutes. Drain and rinse with cold water, then set aside.

In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat. Add the cubed boneless chicken breasts and cook for about 6–8 minutes until golden brown and cooked through. Stir occasionally.

Remove the chicken from the pan and set it aside. In the same skillet, add more oil if needed, then add the chopped bell peppers and julienned carrots. Stir-fry for about 3–4 minutes until vibrant and tender but still crisp.

Return the cooked chicken to the skillet with the vegetables. Add the lo mein noodles, soy sauce, sesame oil, minced garlic, and oyster sauce if using. Toss everything together on medium heat for an additional 2–3 minutes.

Transfer to serving plates or bowls and garnish with fresh green onions. Serve hot and enjoy!