Put the cooked chicken in a food processor, and pulse a few times to roughly chop. Stir, then continue pulsing for another 15 to 30 seconds, until the chicken is finely chopped. (Note: if you turn on the food processor and let it go, you chicken will become a paste instead of finely chopped. So be sure to pulse the chicken for best results.)
In a large bowl, combine the lemon juice, mayonnaise, salt, pepper, and cumin, and blend until thoroughly combined. Add the chicken to the mayo mixture, and fold with a spatula. Next fold in the celery.
Slice the rolls in half horizontally. Top each roll bottom half with a few tablespoons of the chicken salad. Close with the top of the roll.