Prepare the Chicken:
If not already cooked, bake, boil, or sauté the chicken breast until fully cooked, then shred or dice it into bite-sized pieces.

Make the Dressing:
In a large mixing bowl, whisk together the mayonnaise, Dijon mustard, lemon juice, garlic powder, onion powder, salt, and black pepper until smooth and creamy.

Combine the Salad:
Add the shredded chicken, celery, red onion, and sweet pickle relish (if using) to the bowl with the dressing. Stir to combine everything evenly.

Optional Add-Ins:
If desired, fold in the grapes or apple for extra sweetness and texture.

Serve:
Garnish with chopped fresh parsley (if desired) and serve chilled. This salad can be served on bread for sandwiches, in lettuce wraps, or simply on a bed of greens.