Wash the sea bream thoroughly. Mince together the hake, parsley, celery, pepper, preserved lemon and garlic. Heat 1 tablespoon of the sunflower oil in a frying pan, add the mixture, and cook over a low heat, stirring, for 3 minutes. Remove from the pan and leave to cool.
Put the rice, spices, and half the lemon juice in a bowl, then add the cooled hake mixture and combine.
Preheat the oven to 180°C (350°F), Gas Mark 6.
Rub the sea bream with the remaining lemon juice, season with salt and pepper, and drizzle over the remaining olive oil, then fill with the stuffing. Put the remaining sunflower and olive oil in a shallow ovenproof dish, pour in the water, and place the stuffed fish in the casserole. Transfer to the oven and cook for 1 hour.