Start by gathering all your ingredients for the chicken salad sandwich. Chop cooked chicken into small, bite-sized pieces if not already shredded. Wash and dice celery and onion into uniform pieces to ensure an even texture.

In a large mixing bowl, combine the shredded chicken, diced celery, and diced onion. Add in mayonnaise and Dijon mustard, ensuring everything is well-coated for that creamy goodness.

Once the chicken salad mixture is thoroughly combined, season it with salt and pepper to taste. Start with a pinch of each, then mix again, tasting as you go.

While the salad is resting and the flavors deepen, prepare your serving base. If you’re using bread, consider toasting it lightly. Alternatively, wash and dry lettuce leaves.

Take a generous scoop of the chicken salad mixture and place it in the center of your prepared bread or lettuce leaves. Spread it out evenly.

For an extra touch, consider garnishing your chicken salad sandwich with fresh herbs or slices of avocado. Serve immediately.