Season the tuna steaks well, then brush all over with 1 tablespoon of the oil. Mix the remaining oil with the remaining ingredients.
Place the tuna steaks on a lightly oiled baking tray. Top with the tomato mixture. Place in a preheated oven, 220°C (425°F), Gas Mark 7, for 12–15 minutes until the fish is opaque and the tomatoes are lightly charred. Serve immediately with a green salad.