01 - Combine the chicken pieces with all marinade ingredients in a mixing bowl. Mix thoroughly to coat evenly and let marinate for at least 15 minutes at room temperature.
02 - Mix cornstarch and flour in a shallow dish. Dredge each marinated chicken piece in the mixture, pressing gently to ensure an even, thorough coating.
03 - Heat vegetable oil in a deep pan or wok to 350°F. Fry the chicken in small batches until golden brown and crispy, approximately 4–5 minutes per batch. Remove and drain on paper towels.
04 - Heat 2 tablespoons of oil in a large skillet or wok over medium heat. Add sliced onion, red bell pepper, and minced garlic; stir-fry for 2–3 minutes until just tender.
05 - Add the fried chicken to the skillet. Stir in cracked black pepper, green onions, soy sauce, oyster sauce, sugar, and water. Toss quickly and thoroughly until evenly coated and heated through, about 2 minutes.
06 - Transfer to a serving platter while hot. Garnish with additional green onions or fresh cracked pepper if desired.