Score both sides of fish at 2.5 cm
(1 in) intervals and rub with salt and pepper. Leave fish to stand for 25 minutes. Meanwhile, preheat grill. Brush both sides of fish with oil
and grill under a hot grill for about 4 minutes each side until
lightly brown but not burnt. Place on a warmed serving dish. Heat oil in a small pan and stir
fry garlic, ginger, shallots, chilies and spring onion for 1 minute,
then add fish sauce, sugar, tamarind water or lime juice and stock
or water. Bring to the boil and simmer for 30
seconds. Mix corn flour with 1 tablespoon
water and stir into sauce to thicken. Pour sauce over fish.