Rub the cod fillets all over with 1 tablespoon of the oil and season well with salt and pepper. Scatter over the garlic and put the fish in a roasting tin lined with baking paper. Arrange the cherry tomatoes alongside and drizzle with the remaining oil, the balsamic vinegar and basil. Season with salt and pepper to taste.
Cook in a preheated oven, 220°C (425°F), Gas Mark 7, for 12–15 minutes or until the fish is flaky and the tomatoes are roasted. Serve the cod with the tomatoes and rocket leaves.