In a large mixing bowl, combine the shredded chicken, chopped apple, toasted pecans, diced celery, halved grapes, and chopped red onion. Toss gently to mix the ingredients evenly.
In a separate bowl, whisk together the Greek yogurt, Dijon mustard, honey, lemon juice, salt, and pepper until smooth and well combined.
Pour the dressing over the chicken mixture and carefully fold until everything is thoroughly coated.
Taste and adjust seasoning with more salt, pepper, or honey if desired.
Chill the salad in the refrigerator for at least 30 minutes to let the flavors meld together.
Serve the salad over a bed of fresh greens or on its own in a bowl.