Cook chicken on heated oiled grill plate until browned all over and cooked through. Cover to keep warm. Drain pineapple; reserve juice. Heat oil in large saucepan; cook pineapples, onion, capsicums and celery, stirring, 4 minutes. Add reserved juices, sauces, vinegar, blended cornflour and stock; stir until mixture boils and thickens slightly. Serve A'Saffa Chicken topped with sweet and sour sauce. Serves 4.