Place the chicken breasts at the bottom of the crockpot.
Add the chopped onion and frozen mixed vegetables over the chicken.
In a bowl, mix the cream of chicken soup, chicken broth, garlic powder, thyme, salt, and pepper.
Pour the mixture over the chicken and vegetables in the crockpot.
Cook on low for 6 to 8 hours, until the chicken is fully cooked and tender.
Remove the chicken, shred it, and return it to the crockpot.
Stir in the milk to create a creamy broth.
Drop spoonfuls of biscuit dough on top of the mixture.
Cover and cook for an additional 30 minutes on high until the dumplings are cooked through.
Serve hot, garnished with fresh herbs if desired.