Add the chicken, chicken broth, cream of chicken soup, mushrooms, onion, celery, garlic powder, thyme, and pepper to a slow cooker. Stir to combine.
Cover and cook on low for 6-8 hours, or until the chicken is cooked through.
Remove the chicken from the slow cooker and shred it with two forks. Return the chicken to the slow cooker.
In a small saucepan, melt the butter over medium-low heat. Whisk in the flour and cook, stirring constantly, for 1-2 minutes. Slowly whisk in the milk, and cook, stirring constantly, until the mixture is thick and bubbly. Pour the mixture into the slow cooker, stirring to combine.
Add the frozen vegetables and stir to combine. Cover and cook on high for an additional 30 minutes, or until the dumplings are cooked through.
Serve warm.
Interesting Facts
The origin of chicken and dumplings is unknown, but it is believed to have originated in the Southern United States.
The earliest version of chicken and dumplings was made with biscuit dough.
The traditional way to serve chicken and dumplings is over mashed potatoes.