Preheat oven to 450 °F. In a frying pan, heat oil to medium high.Brown the lamb for 5 to 10 minutes along with the harissa and spices. On 4 pitas spread the tomato sauce, vegetables, cheese, lamb and pine nuts. Place on a cookie sheet in the oven for 10 minutes. Finish cooking on broil, and sprinkle with coriander at serving time. Serve with a green salad.