If using raw chicken, cook 2 boneless, skinless breasts in a skillet with salt and pepper until fully cooked (165°F internal temp). Let cool, then dice or shred.
In a large bowl, whisk together mayonnaise, Greek yogurt, Dijon mustard, lemon juice, honey (if using), salt, and pepper.
Add diced chicken, celery, grapes, red onion, and parsley to the bowl. Gently fold everything together until evenly coated.
Cover and refrigerate for at least 30 minutes to let flavors meld. Serve on croissants, bread, or over a bed of greens.
