Combine mayonnaise and garlic powder. Separate each pita round into 2 rounds. Spread mayonnaise mixture evenly on inside of split rounds. Arrange chicken strips evenly down centers of pita rounds; top evenly with lettuce, tomato, and cucumber. Fold over left and right sides of pita rounds to partially enclose filling. Fold short sides over to form rectangles.
Coat a nonstick skillet with cooking spray. Place over medium-high heat until hot. Sprinkle 1 tablespoon water in skillet. Place 2 sandwiches, seam sides down, in skillet; press firmly. Cook 2 to 3 minutes or until lightly browned. Turn sandwiches; press firmly, and cook 2 additional minutes or until lightly browned. Wrap in wax paper, and keep warm. Repeat procedure.