Potato, apple and tuna frittata

Heat the oil in a non-stick frying pan, add the apple pieces and cook for 5 mins, or until they soften slightly. Add the potatoes, and then cook for a few minutes to take a little colour. Sprinkle on the raw onion and tuna fish. In a bowl, whisk together the eggs, milk, and oregano then season well. Pour over the potato mixture, sprinkle on the cheese and place under a hot grill or into a hot oven (200C, gas mark 6) until risen and set, about 5-8 mins. Cut into wedges, and serve hot or cold with a blob of mayonnaise.