Toast the cumin seeds in a dry pan for 2-3 minutes over low heat. Grind to a powder in a mortar and pestle or in a spice grinder and set aside.
Seed the chilies and cut into julienne strips.
Place half of the olive oil in one large frypan and half in a nonstick pan with a lid. Put the potato into the nonstick pan. Add the tumeric and fry, tossing and turning the potatoes.
At the same time in the other pan, fry the onion and celery, stirring occasionally. When the onion begins to soften, add the garlic, lime leaves, chiles, cumin, paprika and saffron. Cook for a further 2-3 minutes, then season lightly with salt and pepper and turn off the heat. Leave in the pan while the potatoes finish cooking.
As soon as the potatoes are cooked, season the fish steaks with salt and pepper and put them on top of the potatoes. Spoon the onion mixture over and around the steaks and pour over the tomatoes. Bring to boil over a medium-high heat, immediately lower it and cover. Cook gently for 7-10 minutes or until the fish is just cooked. Taste and season.
Serve in large warmed bowl, sprinkled with cilantro.
Recipe courtesy Everyday Epicurean by Catherine Bell (Ten Speed Press, 2000); Photograph by Kieran Scott