About 10 minutes before serving, heat pita bread folds as directed on package. Meanwhile, remove chicken from cooker; place on plate. Stir yogurt into onion mixture. Shred chicken by pulling apart with 2 forks. Spoon chicken onto warm pita breads. Spoon onion mixture, using slotted spoon, onto chicken. Top with tomato and cucumber. Fold pita breads in half to serve.