For the marinade, strip the thyme leaves into a non-metallic dish with the oil and lemon juice. Season the tuna, then add to the dish. Cover and marinate for one hour, turning once.
Put the tomatoes, sweetcorn, coriander, onion, and pepper in a bowl. Squeeze one of the limes into the mixture and season. Leave to stand.
Heat a griddle pan. Cook the tuna for two to three minutes, turn, and brush with marinade. Griddle for two to three minutes more. The tuna should be rare in the centre.
Put the tuna on to four warmed plates. Serve the salsa and lime wedges on the side.
- 4 skinless tuna steaks, about 250g each
- Salt and freshly ground black pepper
- 4 tomatoes, skinned, deseeded, and chopped
- 200g canned sweetcorn, drained
- Leaves from 1 bunch of coriander, finely chopped
- 1 onion, chopped
- 1 red pepper, diced
- 2 limes
For the marinade
- 2–3 sprigs of thyme
- 2 tbsp vegetable oil
- Juice of 1⁄2 lemon