In 3- to 4-quart slow cooker, mix chili beans and onion. Top with turkey. Sprinkle taco seasoning over turkey; spoon salsa over top.
Cover; cook on Low heat setting 7 to 9 hours.
Place turkey on cutting board. Remove meat from bones; discard bones. Using 2 forks, pull turkey into shreds. Stir turkey into bean mixture in cooker.
Heat taco shells as directed on package. Spoon turkey mixture into taco shells. Top with lettuce, tomato and cheese.