Put 3 tbsp olive oil into a food bag and add 4 tuna steaks tuna steaks. Rub well together and leave for 30 mins while you make the relish. Peel ½ cucumber, halve lengthways and scoop out the seeds. Chop the flesh into small dices. Mix with 2 spring onions finely chopped, 1 med tomato finely chopped, ½ large red chilli seeded and finely chopped, 1 tbsp olive oil, 2 tbsp chopped parsley, 1 tbsp lime or lemon juice, season to taste. Set aside. Grill to desired doneness. Remove the steaks from the grill allow to stand for 3-5 mins, then spoon over the relish and serve.