Cook the pasta in boiling salted water until tender. Meanwhile, in a large saucepan, heat the oil and fry the onion and garlic until softened. Add the chicken and continue to fry until just browned. Pour in the passata, tomatoes, olives, herbs and seasoning. Leave to simmer gently for 5 minutes or until the chicken is cooked through. Drain the cooked pasta and mix with the chicken mixture. Stir in half the cheese. Pour into an ovenproof dish and layer the remaining cheese on top. Place under a preheated grill for 10 minutes, until the cheese has melted. Serve immediately with a leafy green salad.