Bring chicken stock and water to a boil in a large pot. Add linguine and serrano pepper; cook until linguine is tender yet firm to the bite, about 10 minutes.
Stir napa cabbage, kielbasa sausage, onion, and mushrooms into the pot. Simmer, stirring occasionally, until onion softens and kielbasa is heated through, 8 to 10 minutes.
Season soup with salt and white pepper. Serve garnished with cilantro.
