01 - In a large bowl, combine the chicken pieces with soy sauce, vinegar, ginger-garlic paste, cornstarch, all-purpose flour, black pepper, salt, and egg. Mix thoroughly to coat every piece evenly. Let the chicken marinate for at least 15 minutes.
02 - Heat oil in a deep pan or wok over medium-high heat. Fry the marinated chicken pieces in batches until golden and crispy, about 3–5 minutes per batch. Remove with a slotted spoon and drain on paper towels.
03 - In a large wok or skillet, heat 3 tbsp oil. Add chopped garlic, green chillies, and onion. Sauté for 1–2 minutes until fragrant and slightly softened.
04 - Add the diced bell peppers and white parts of the spring onions. Stir-fry for another 2 minutes, keeping the vegetables crisp-tender.
05 - In a small bowl, whisk together soy sauce, chilli sauce, tomato ketchup, oyster sauce, sugar, and water until well combined.
06 - Pour the sauce mixture into the wok with the vegetables. Stir well and bring to a simmer. Add the fried chicken pieces and toss to coat evenly in the sauce.
07 - Pour in the cornstarch slurry and stir quickly as the sauce thickens and forms a glossy glaze over the chicken.
08 - Garnish with reserved spring onion greens. Serve hot with steamed rice or fried rice.