1.In A Large Nonstick Skillet Coated With Nonstick Cooking Spray, Cook Chicken Over Medium Heat For 10-12 Minutes On Each Side Or Until Juices Run Clear. Remove; Thinly Sliced Chicken And Cool. 2.Meanwhile, In A Small Bowl, Combine The Yogurt, Mayonnaise, Mustard, Cumin And Cayenne; Set Aside. In A Large Bowl, Combine The Spinach, Cucumber, Onions And Chicken. Drizzle With Yogurt Mixture; Toss To Coat. Microwave Pita Breads For 15-20 Seconds Or Until Warmed. Fill Each Half With 1/2 Cup Chicken Mixture.