Heat the oil in a non-stick frying pan. Sauté the onion and garlic. Add the curry paste and cook briefly. Pour in the coconut milk and bring to the boil. Reduce the heat, simmer the liquid for approx. 7 mins., season. Add the fish fillets and gently simmer for approx. 5 mins. Spoon the sauce over the fillets from time to time. Plate up the fish curry and garnish with coriander.