Cook chicken in an ovenproof nonstick skillet over medium-high heat until brown. Bake at 350° for 10 to 12 minutes or until done. Cool slightly, and thinly slice.
Whisk together yogurt and next 4 ingredients in a large bowl; add chicken, cucumber, green onions, and spinach, tossing to coat.
Bake pita halves at 200° for 3 to 4 minutes. (Do not toast.)
Spoon filling evenly into pita halves.