Method
In a large mixing bowl, combine the diced apples, halved grapes, sliced celery, and toasted walnuts.
In a separate small bowl, whisk together the mayonnaise, Greek yogurt, lemon juice, honey, salt, and black pepper until smooth and well combined.
Pour the dressing over the apple mixture and gently toss with a spatula until all ingredients are evenly coated.
Taste and adjust seasoning with additional salt, pepper, or honey if desired.
Cover the salad tightly with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld.
Serve chilled in individual bowls or on a platter, garnished with additional toasted walnuts if desired.