In a large bowl beat the eggs with chopped parsley, pepper and salt. In a large frying pan fry the onion wedges over a high heat for about 4 mins until they start to brown, mix in tomatoes and olives and cook for 1-2 mins until the tomatoes begin to soften. Turn the heat down to medium and pour in the eggs. Cook the eggs in the pan, stirring them as they begin to set, until half cooked, but still runny in places – about 2 mins. Scatter over the feta, then place the pan under the grill for 5-6 mins until omelette is puffed up and golden. Cut into wedges and serve straight from the pan.