In a large mixing bowl, combine the shredded rotisserie chicken with the diced celery and red onion.
In a separate small bowl, whisk together the mayonnaise, lemon juice, Dijon mustard, and garlic powder until smooth and well combined.
Pour the dressing over the chicken mixture and stir until everything is evenly coated.
Fold in the chopped pecans and fresh dill, then season with salt and black pepper to taste.
Cover and refrigerate for at least 30 minutes before serving to allow the flavors to meld together.
Serve over lettuce cups, with cucumber slices, or enjoy on its own.