Make the sauce up to 2 days in advance. Arrange the tomatoes in a roasting tin, season well and cook in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes.
Transfer the tomatoes and any cooking juices to a pan and heat through gently with the lemon juice and rind. Season to taste and set aside until ready to serve.
Season the fish fillets and cook under a preheated hot grill for approximately 10 minutes or until the fish is cooked through.
Meanwhile, warm the sauce through. Stir the basil and oil through the sauce and spoon it over the fish. Garnish with basil leaves, more grated lemon rind and lemon wedges.