01 - In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, rice vinegar, freshly ground black pepper, corn starch, and water until smooth. Set aside.
02 - Heat the vegetable oil in a large wok or skillet over high heat until the oil begins to shimmer.
03 - Add the thinly sliced chicken to the hot wok in a single layer. Stir fry for 3 to 4 minutes, turning occasionally, until the chicken is golden and cooked through. Transfer the chicken to a plate and set aside.
04 - Return the wok to the heat and add the sesame oil. Toss in the sliced onion and all three bell peppers, stir frying for 2 to 3 minutes until tender-crisp. Add the minced garlic and cook for an additional 30 seconds until fragrant.
05 - Return the cooked chicken to the wok. Pour in the prepared sauce and toss everything together vigorously. Stir fry for 2 to 3 minutes until the sauce thickens and evenly coats the chicken and vegetables.
06 - Remove from heat and garnish with sliced spring onions. Serve immediately alongside steamed jasmine rice or noodles.