Clean, wash, and prepare the fish by cutting it in pieces.
In a bowl mix together the finely chopped thyme, grated tomatoes, season with salt and pepper, and squeezed lemon juice.
Transfer the fish to the mixture and leave it aside for half an hour.
Place in a pot with water carrots, chopped onions, celery, hot peppers and oil, and boil them until soft.
Transfer the fish pieces and the soup in clay pot and boil for another 20 minutes.
Serve fish soup sprinkled with pepper and lemon slices.