Place the chicken breasts in the bottom of the slow cooker.
Add the carrots, celery, and onion on top of the chicken.
Pour in the chicken broth and stir in the thyme, garlic powder, salt, and pepper.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours, until the chicken is cooked through and tender.
Once the chicken is cooked, remove it from the slow cooker and shred it with two forks.
Return the shredded chicken to the slow cooker.
Stir in the cream of chicken soup and frozen peas.
In a separate bowl, mix the biscuit mix and milk until just combined.
Drop spoonfuls of the biscuit mixture over the chicken mixture in the slow cooker.
Cover and cook on high for an additional 30 minutes, or until the biscuits are cooked through.
Serve hot and enjoy!