Spray 3- to 4-quart slow cooker with cooking spray. Place chicken thighs in cooker. Sprinkle with taco seasoning mix and brown sugar; toss to coat. Mix in green chiles, corn and 1/2 cup of the enchilada sauce. Refrigerate remaining enchilada sauce.
Cover and cook on Low heat setting 6 to 7 hours.
Place chicken on cutting board; use 2 forks to pull chicken into shreds. Return chicken to cooker. Stir in green onions. Cover and cook on Low heat setting 15 minutes.
Heat remaining enchilada sauce. Serve chicken mixture in taco shells with lettuce, tomatoes and warm enchilada sauce.