In a large bowl, combine the juice of 1 lemon, the mayonnaise, salt, and pepper.
Make the chicken salad:
Remove the meat from the rotisserie chicken, discarding any skin and bones. Coarsely chop the chicken into pieces and add them into the bowl as you go.
Add the chopped celery and shallot (or red onion) to the chicken bowl. Toss to combine the chicken salad with the dressing, until all pieces are coated well.
Chill & serve:
The chicken salad can be enjoyed immediately or after chilling for 1 hour in the fridge to let it absorb the lemon flavor.
Storage:
Refrigerate any leftover chicken salad for up to 4 days. I do not recommend freezing because the texture changes.