Cook the Chicken: Start by cooking the chicken breasts if you haven't already. You can boil, bake, or grill them. Once cooked, let the chicken cool and then shred or dice it into small pieces.
Prepare the Mix-Ins: Finely chop the celery, onion (if using), and hard-boiled egg. If using pecans, chop them into small pieces.
Combine Ingredients: In a large mixing bowl, add the shredded or diced chicken, chopped celery, onion, egg, sweet pickle relish, and chopped pecans.
Add Mayonnaise: Add the mayonnaise to the bowl and stir until all the ingredients are well coated. Start with 1/2 cup of mayonnaise and add more if you prefer a creamier texture.
Season: Add salt, pepper, garlic powder, and lemon juice (if using) to taste. Mix well to ensure all the flavors are evenly distributed.
Chill: Cover the bowl and refrigerate the chicken salad for at least 1 hour before serving. This allows the flavors to meld together.
Serve: Serve the chicken salad on a bed of lettuce, in a sandwich, or with crackers.