Spray 3 1/2- to 4-quart slow cooker with cooking spray. Spray 10-inch skillet with cooking spray. Add turkey, onion and celery; cook over medium-high heat 5 to 7 minutes, stirring occasionally, until turkey is no longer pink. Drain.
In slow cooker, stir together turkey mixture, cooking sauce, brown sugar, Worcestershire sauce and grill seasoning.
Cover; cook on Low setting 3 to 4 hours. Stir; spoon turkey mixture into buns. If desired, season to taste with salt and pepper.