In a large mixing bowl, take 3 cups of finely chopped or shredded cooked chicken. Add in ½ cup of finely diced celery, ¼ cup of finely diced red onion, and 2 tablespoons of finely chopped Italian parsley. Gently stir all the ingredients together until well mixed.

In a separate small bowl, whisk together ¾ cup of mayonnaise, 1 tablespoon of Dijon mustard, 1 tablespoon of fresh lemon juice, ½ teaspoon of kosher salt, ½ teaspoon of garlic powder, and ¼ teaspoon of black pepper until smooth.

Pour the dressing over the chicken mixture. Use a spatula to gently fold the dressing into the chicken until every piece is coated.

Cover with plastic wrap or transfer to an airtight container and refrigerate for at least 30 minutes.

Serve on sliced bread or atop lettuce with toppings such as leafy greens or sliced tomatoes.