Heat the oil in a large, deep frying pan, about 25 cm in diameter, with a flameproof handle. Add the capsicum and leek and fry gently for 10 minutes until softened. If you are using the olives, toss them into the mixture, then add the chicken and the cooked pasta, ensuring all the ingredients are well mixed.
Preheat a grill to a moderate heat. Beat the eggs with the chopped parsley and season well. Pour into the hot pan and swirl around to allow the eggs to settle evenly. Cook over a moderate heat for 4–5 minutes, or until nearly set.
Arrange the slices of cheese over the top of the frittata. Place under the grill for 5 minutes, or until the cheese melts and bubbles.
Slide the frittata onto a hot plate and cut into wedges to serve. It can be eaten warm or cold.