Cut the skin and the white membrane off the orange. Working over a bowl to catch the juice, cut between the membranes to remove the segments. Halve the segments and mix them with the reserved juice and the garlic, tomatoes, basil, olives and 4 tablespoons of the oil. Season to taste with salt and pepper and set aside to infuse.
Brush the cod with the remaining oil and coat with the jerk seasoning. Heat a large, heavy-based frying pan and cook the cod, skin-side down, for 5 minutes. Turn the fish over and cook for a further 3 minutes. Transfer to a preheated oven, 150°C (300°F), Gas Mark 2, to rest for about 5 minutes. Garnish the fish with basil and serve with the salsa and a green salad.