Place the chicken breasts at the bottom of the slow cooker.

Add diced carrots, celery, onion, and minced garlic over the chicken.

Pour in the chicken broth, and add thyme, rosemary, black pepper, and salt. Stir to combine.

Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is cooked through and tender.

Once the chicken is cooked, shred it in the slow cooker using two forks and mix it back into the soup.

In a medium bowl, mix together the flour, baking powder, and salt.

Stir in the milk and vegetable oil until just combined to form a dough.

Drop spoonfuls of the dough over the chicken mixture in the slow cooker.

Cover and cook on high for an additional 30-40 minutes, until the dumplings are fluffy and cooked through.

Stir in the frozen peas and let them heat through for a few minutes before serving.