Follow the steps in order for the best result.
In the base of your slow cooker, add the chopped onion, celery ribs, carrots, minced garlic, kosher salt, and black pepper.
Arrange the bite-sized cooked chicken pieces over the vegetables, followed by the rinsed barley, butter, chicken broth, water and chicken bouillon cubes. It is important to not stir the ingredients at this point.
Cover the slow cooker with the lid and set it to cook on the LOW setting for 8 hours.
Just before you are ready to serve the soup, stir in the chopped fresh parsley and Tabasco sauce.