Prepare the Ingredients : Thinly slice the chicken and set aside. Trim the green beans and julienne the carrot, if using. Slice the onion and mince the garlic.

Make the Sauce : In a small bowl, combine the oyster sauce, soy sauce, sesame oil, cornstarch, water, and sugar (if using). Mix well and set aside.

Stir-Fry the Chicken : Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high heat. Add the chicken slices and stir-fry for 3–4 minutes, or until just cooked through. Remove the chicken and set aside.

Cook the Vegetables : In the same pan, add the remaining tablespoon of oil. Add the green beans, carrots (if using), and onion. Stir-fry for 2–3 minutes, until the vegetables are slightly tender but still crisp. Add the minced garlic and stir-fry for an additional 30 seconds.

Combine and Serve : Return the chicken to the pan with the vegetables. Pour the sauce over the mixture and toss everything together. Stir-fry for another 1–2 minutes, allowing the sauce to thicken and coat the chicken and vegetables evenly. Remove from heat and serve hot over steamed rice or noodles for a complete meal.