In the dish of a slow cooker, combine the chicken breast pieces, onion, celery, chicken broth, garlic powder, thyme, salt, pepper, and carrots. Cover with the lid and cook for 4 hours on high, or 6 on low.
In the final 30 minutes, prepare your favorite biscuits.
In a small bowl, whisk the water with the cornstarch until just combined. Add the mixture to the slow cooker along with the green peas and half and half. Stir and cook on low for an additional 30 minutes.