Cut the fish into pieces about 5 cm in size. Sprinkle with salt, drizzle with the lime juice and set aside for 20 minutes.
Heat the oil in a deep saucepan. Pat the fish dry. Fry several pieces at once until they are lightly browned on the outside and just cooked through. Drain on kitchen paper.
When the fish pieces are deep-fried, pour off the oil except for 2 ½ tablespoon. In the remaining oil, fry the onion and garlic until they are soft and colored. Add the coconut milk, soy sauce and curry paste and bring to the boil. Simmer for 2 minutes, then add the fish and let steep for 3-4 minutes. Season to taste with salt and lemon juice.