Clean fish and make criss-cross slashes on both sides of the fish. Dab dry and rub salt on both sides of the fish. Coat lightly with tapioca flour then deep-fry in medium hot oil until golden. Place fish on a serving plate.
Fry chopped garlic until golden and crispy. Dish out and set aside. In remaining hot oil fry kaffir lime leaves until fragrant and crispy. Dish out.
Leave 3 tablespoons of oil in the wok. Add dried chillies and Szechuan peppercorns. Fry for a while until oil turns spicy. Strain the oil and put it back into the wok.
Add combined fragrant sauce ingredients and bring to a boil. Drizzle in cornflour mixture to thicken the sauce. Add a little of the fried kaffir lime leaves.
Pour the sauce over the fish and garnish with the rest of the fried crispy kaffir lime leaves and crispy garlic. Serve at once.