Wash the fish thoroughly, then slash twice on both sides.
Prepare a marinade with the tomatoes, celery, parsley, lemon rind, garlic, turmeric, pepper, salt to taste and a large glass of water. Add half the mixture to the cooked rice with half the olives. Fill the fish cavity with this stuffing.
Preheat the oven to 180°C (350°F), Gas Mark 6.
Pour the oil and the remaining marinade into a roasting tin and place the fish in the middle with the sliced potatoes around it. Stir well to coat the potatoes in the marinade. Transfer to the oven and cook for 1 hour. Serve garnished with the remaining olives.