Prepare the chicken: Chop or shred the cooked chicken into small, bite-sized pieces.
Chop the vegetables: Finely chop the celery and slice the green onions.
Make the dressing: Stir together the mayonnaise, Dijon mustard, lemon juice, and garlic powder until smooth.
Season the dressing: Add salt and black pepper, then taste and adjust if needed.
Combine the ingredients: Place the chicken, celery, green onion, and optional pecans in a large bowl.
Add the dressing: Pour the dressing over the chicken mixture.
Mix gently: Stir until the chicken and vegetables are evenly coated without overmixing.
Chill: Cover and refrigerate for about 30 minutes so the flavors can come together.
Serve: Stir once more and serve in lettuce cups, over greens, or with keto-friendly sides.