In a large bowl, combine the shredded chicken, halved grapes, diced celery, and toasted almonds.
In a small bowl, whisk together the Greek yogurt, mayonnaise, lemon juice, Dijon mustard, salt, and pepper until smooth.
Pour the dressing over the chicken mixture and stir gently until everything is evenly coated.
Taste and adjust seasoning with more salt or lemon juice if needed.
Cover the bowl and refrigerate for at least 30 minutes to let the flavors meld.
Serve chilled on bread, lettuce cups, or with crackers. Garnish with fresh herbs if desired.