Heat the oil in a frying pan, add the red peppers and onion and sauté gently until just soft. Add the garlic, vinegar, tomato purée, thyme and fish stock. Simmer for 5 minutes, then season to taste.
Turn the mixture into a food processor or blender and purée until smooth, then transfer to a flameproof casserole. Add the celery and swordfish and bring to the boil. Cover and bake in a preheated oven, 350°C (175°F), Gas Marie 4, for 20—30 minutes.
Meanwhile, put the rice into a saucepan, add the water, season with salt and bring to the boil. Lower the heat, cover the pan and simmer for 12—14 minutes or until the rice is tender and all the liquid has been absorbed.
Drain the rice and fluff up with a fork, stir in the black olives and keep warm. Transfer the fish to a warmed serving dish and serve with the rice and sprinkled with thyme.