In a small bowl, toss the diced apple with 1 tablespoon of the lemon juice to prevent browning.
In a large bowl, whisk together the mayonnaise, remaining lemon juice, lemon zest, Dijon mustard, salt, and pepper until smooth.
Add the diced chicken, apple, celery, red onion, and fresh herbs to the bowl. Stir until everything is evenly coated.
If using nuts, fold them in gently.
Taste and adjust seasoning with more salt, pepper, or lemon juice as desired.
Cover and refrigerate for at least 30 minutes before serving to allow flavors to meld.
Serve chilled on bread, lettuce cups, or with crackers.