01 - Combine shredded chicken, Caesar dressing, Parmesan, lemon juice, Dijon mustard, celery, and red onion in a large bowl. Mix thoroughly until all ingredients are evenly coated. Season generously with salt and pepper to taste.
02 - Slice each croissant horizontally without cutting completely through, creating a hinged pocket for easy filling.
03 - Layer chopped romaine lettuce along the bottom half of each opened croissant to create a crisp foundation.
04 - Spoon a generous portion of the chicken Caesar salad mixture onto the lettuce bed, distributing evenly among all four sandwiches.
05 - Top with additional Parmesan shavings if desired. Gently close the croissants and serve immediately for optimal texture.