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