In a slow cooker, add chicken breasts and top with ½ cup wing sauce and onions. Cover and cook on low for 6-7 hours or high for 4-5 hours.
Remove chicken from slow cooker and shred using 2 forks or stand mixer. Reserve ¼ cup of liquid from slow cooker, and discard the rest. Place shredded chicken back into slow cooker bowl, add ¼ cup reserved liquid, and remaining ½ cup wing sauce. Stir to coat chicken.
Place about ¼ to ⅓ cup of chicken on each bun. Garnish with additional wing sauce and ranch dressing if desired. Enjoy!
