Mix yogurt, salt, pepper and garlic in a bowl. Mix chicken with yogurt and marinate
1 to 2 hours at room temperature, up to 2 days refrigerated.
Thread chicken on skewers and grill over medium hot coals.
Place warmed pita bread on plates (if using tortillas, toast briefly over flame),
divide meat among them, top with tomato and onion slices and cilantro and fold bread
over. Serve with lemon or lime quarters for squeezing.