Step 1: Coat the Chicken in Batter — In a large bowl, combine the chicken cubes with the ginger garlic paste, soy sauce, red chili powder, black pepper, and salt; mix well and rest for 15 minutes. Then add the cornflour, all-purpose flour, and beaten egg. Mix thoroughly, adding water a tablespoon at a time until every piece is coated in a thick, sticky batter — it should cling, not drip. Dust with the extra 2 tablespoons of cornflour for an extra-crisp crust.
Step 2: Fry Until Golden and Crisp — Heat 2–3 inches of oil in a deep kadhai or wok over medium-high heat (about 350°F / 175°C — a drop of batter should sizzle and rise immediately). Fry the chicken in batches, without crowding, for 4–5 minutes per batch, turning once, until deep golden and crisp. Drain on a wire rack or paper towels. The coating should be crunchy — this is what survives the saucy toss without going soggy.
Step 3: Char the Peppers and Onions — In a large wok or heavy skillet, heat the 2 tablespoons of oil over the highest heat you have. Add the julienned ginger, chopped garlic, and slit green chilies; stir-fry for 20 seconds until fragrant. Add the cubed onions and both capsicums. Toss for 2–3 minutes — you want them charred at the edges but still crunchy. This high-heat char is the soul of restaurant-style chilli chicken; don't lower the flame.
Step 4: Build the Sauce — Push the vegetables to the sides of the wok. In the center, add the soy sauce, red chili sauce, ketchup, vinegar, sugar, black pepper, and a pinch of salt. Let the sauces sizzle and caramelize for 30 seconds, then toss everything together so the vegetables are coated in a glossy, dark-red glaze.
Step 5: Toss the Chicken — Add the fried chicken pieces to the wok along with the spring onion whites. Toss everything vigorously over high heat for 1–2 minutes until each piece is lacquered with sauce. If the mixture looks dry, splash in 2 tablespoons of hot water — it should be glossy, not soupy. This is dry-style chilli chicken: every piece glistening, no pooling sauce.
Step 6: Garnish and Serve — Transfer to a serving platter, shower with the reserved spring onion greens, and serve immediately while the chicken is still crisp and the vegetables are hot and crunchy.