In 12-inch nonstick skillet, heat oil over medium-high heat. Add turkey and onion; cook 6 to 9 minutes, stirring occasionally, until turkey is no longer pink. Drain.
Meanwhile, spray 3 1/2- to 4-quart slow cooker with cooking spray. In cooker, mix remaining ingredients except buns; stir in turkey mixture.
Cover; cook on Low heat setting 4 to 5 hours.
Fill buns with 1/3 cup turkey mixture each.