Spray 3- to 4-quart slow cooker with cooking spray. Remove netting or strings from pork roast; cut pork into 2-inch pieces. Place pork and onion in cooker. Sprinkle with jerk seasoning; toss to coat. Pour chili sauce over top.
Cover and cook on Low heat setting 9 to 11 hours.
Place pork on cutting board; use 2 forks to pull pork into shreds. Return pork to cooker. Mix corn relish and cilantro in small bowl. To serve, layer lettuce, pork mixture and corn relish in pita fold breads.