Cook and cool turkey, then shred or dice it
Chop celery, onion, and any other desired add-ins
In a bowl, mix mayonnaise, salt, pepper, and a little mustard or lemon juice
Add the turkey and chopped vegetables to the bowl
Stir until everything is evenly coated
Taste and adjust seasoning if needed
Serve chilled on bread, crackers, lettuce, or in a wrap