01 - In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, rice vinegar, black pepper, corn starch, and water until smooth. Set aside.
02 - Heat vegetable oil in a large wok or skillet over high heat until the oil just begins to shimmer.
03 - Add the sliced chicken in an even layer and stir fry for 3–4 minutes until golden and cooked through. Transfer to a plate and set aside.
04 - In the same wok, add sesame oil. Stir fry the onion and bell peppers for 2–3 minutes until tender-crisp. Add minced garlic and cook for 30 seconds until fragrant.
05 - Return the chicken to the wok, pour in the prepared sauce, and toss everything together. Stir fry for 2–3 minutes until the sauce thickens and evenly coats the chicken and vegetables.
06 - Transfer to a serving platter, garnish with sliced spring onions, and serve immediately with steamed rice or noodles.