Arrange pita on a baking tray and lightly toast under the grill. Cut pittas into bite-size pieces and keep warm.
Heat the olive oil in a frying pan over medium heat. Stir in the chicken, onion and garlic and cook until chicken juices run clear. Pour in passata and season with cumin, salt and pepper. Continue cooking 10 minutes.
Arrange pita pieces in a serving dish. Drizzle with butter and top with the chicken mixture. Garnish with dollops of yoghurt and parsley to serve.