Mix together the oil, lemon rind, parsley and coriander seeds with plenty of pepper in a non-metallic dish. Add the tuna steaks and coat evenly with the mixture. Leave to marinate while you make the salsa.
Make the salsa by mixing together all the ingredients in a bowl. Season to taste with salt and pepper and set aside for the flavours to infuse.
Heat a ridged griddle pan or frying pan until hot, add the tuna steaks and cook for 1–2 minutes on each side or until seared all over. The tuna should be well seared but rare. Remove from the pan and leave to rest for 2–3 minutes.
Serve the tuna steaks with a spoonful of salsa, a dressed salad and plenty of fresh crusty bread.