SPRINKLE dressing mix evenly over chicken. Refrigerate 10 minutes. Place chicken in 15x10x1-inch baking pan sprayed with cooking spray.
BAKE at 350°F for 20 to 25 minutes or until cooked through. Cut chicken into strips.
MIX yogurt, cucumber, onion, mint and oregano in large bowl. Add chicken and lettuce; mix lightly. Spoon into pita halves; sprinkle with cheese.