Heat oil in Dutch oven over medium-high heat until shimmering. Add ground chicken, onion, carrot and celery. Cook 5-10 minutes, stirring often, until chicken is no longer pink, but not browned.
Reduce heat to medium-low. Add water, broth, bay leaves, salt and chicken breasts. Cover and cook 30 minutes. Remove lid, increase heat to high and bring to a boil. (If liquid is already boiling when lid is removed, remove chicken breasts immediately and proceed.) Transfer chicken breasts to a plate and set aside. Adjust heat to maintain gentle boil and cook an additional 20 minutes. Strain stock through fine-mesh strainer, pressing on solids to extract as much liquid as possible, then discard solids. Allow stock to stand 5 minutes, then skim off most of the fat (leave a tablespoon or two behind for flavor). (Stock can be refrigerated 2 days or frozen up to 3 months at this point. Store chicken breasts in a ziplock bag with the air squeezed out and stock in an airtight container.).
To make soup from the stock, return stock to Dutch oven over medium-high heat. In a small bowl, combine cornstarch with cold water until smooth. Stir slurry into hot stock and bring to gentle boil. Add onion, carrot, celery and potato. Cook until potato is almost tender, 10-15 minutes. Adjust heat as needed to keep at a gentle boil. Add egg noodles and cook another 5 minutes or until noodles and all vegetables are tender.
Meanwhile, remove skin and bones from chicken breasts. Shred meat with fingers or two forks and return to stock. Add parsley and cook until chicken is heated through, about 2 minutes. Adjust seasoning with salt and pepper and serve.