Place the tomatoes in boiling water for about 10 seconds. Drain and pull away the skin. Cut away the core and discard. Cut the tomatoes crosswise and then cut into small cubes. Set aside.
04Heat the remaining oil in a saucepan over medium-high heat. Add the onion and cook, stirring, until wilted. Add the garlic, turmeric, capers, lemon juice and rind, tomatoes, cayenne, salt and pepper. Cook, stirring, 3 minutes. Set aside and keep warm.05Place the mackerel fillets skin side up under the broiler and cook about 3 minutes. Carefully flip the fillets and cook another 3 to 4 minutes until the fish is cooked through.06Transfer the fillets to a warm serving plate and spoon equal portions of the tomato-caper sauce over them. Sprinkle with parsley and serve immediately.