Simmer chicken in a pot of water over medium heat to an internal temperature of 165°F. Remove from water. Dice chicken into small bitesized pieces and refrigerate to cool fully.
Once cooled, thoroughly mix the chicken, celery, onion, and mayo, in a bowl. Season with salt and pepper to taste.
Lightly toast the bread.
Layer the roll with chicken salad, cheese, spring mix, and tomato seasoned with salt and pepper. Cut in half and serve with chips and pickles.