Score the fish and rub lightly with salt and pepper.
Grind the lemongrass, ginger, garlic and chilies into a coarse paste.
Heat the cooking oil and deep fry the fish, turning if not completely submerged in oil, about four minutes per side or until deep golden and crisp on the outside.
Drain the fish and keep warm.
Pour off the oil from the pan leaving only about two tablespoonfuls.