1. In a large saucepan, add chicken stock, chicken breast (no need to chopped it yet), carrots, celery, onion, and garlic. Bring to a boil and simmer until chicken is fully poached, about 20 minutes.
2. Remove chicken breast with a slotted spoon and place on a cutting board. Chop chicken into very small pieces and return to pot with vegetables and pasta, if using. Simmer everything until veggies are cooked through. Add salt and pepper to taste.