01 - Combine cooked chicken, celery, red onion, mayonnaise, Dijon mustard, dill, parsley, lemon juice, salt, and pepper in a mixing bowl. Mix thoroughly until all ingredients are evenly distributed.
02 - Use a vegetable peeler or mandoline to slice cucumbers lengthwise into thin, wide ribbons. Discard the initial slice containing mostly skin. Create ribbons that are pliable yet substantial enough to hold filling.
03 - Pat cucumber ribbons dry with paper towels to eliminate surface moisture. This step ensures the filling adheres properly and prevents sogginess.
04 - Lay a cucumber ribbon flat on a clean work surface. Spread approximately 1 tablespoon of chicken salad mixture along one short end. Add a spinach leaf if desired.
05 - Gently roll the cucumber around the filling, creating a tight cylinder. Place seam side down on a serving platter. Repeat with remaining ingredients. Chill for 10 minutes before serving to allow flavors to meld.