Instructions:
- Prep Chicken & Nuts (If using): Ensure chicken is fully cooked and cooled. Shred or dice it into bite-sized pieces. If using nuts, lightly toast pecans/walnuts in a dry skillet until fragrant (2-3 minutes); set aside to cool completely.
- Combine Solids: In the large mixing bowl, combine the shredded chicken, diced celery, halved grapes, minced red onion, toasted nuts (if using), and chopped tarragon. Gently toss to distribute.
- Whisk the Dressing: In a separate small bowl, whisk together the mayonnaise, Dijon mustard, lemon juice, apple cider vinegar, salt, and pepper until smooth and homogenous. Taste and adjust seasoning now.
- Dress the Salad: Pour the dressing over the chicken mixture. Using a rubber spatula, gently fold the ingredients together until everything is just coated. Be careful not to overmix.
- Chill & Serve: Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld. Serve cold on lettuce cups or in sandwiches.