Combine cumin and chili powder in a plastic bag. Add chicken and shake to coat. Heat 1 tablespoon oil in a large skillet over medium heat. Add chicken; cook 5 minutes or until chicken is no longer pink, stir frequently. Take off heat, set aside to cool.

Combine remaining ingredients except pita pockets, mixing well. Stir in chicken. Add salt and pepper. Cut top off pitas to open. Divide chicken mixture among the pitas; top with yogurt, if desired.