Heat the oil in a large pot over medium heat. Add the onion, garlic, carrots, and celery. Cook, stirring occasionally, until the vegetables have softened, about 5 minutes.
Add the chicken broth, miso paste, mirin, soy sauce, sake, and sesame oil. Bring to a simmer and cook for 10 minutes.
Stir in the cooked chicken and simmer for 10 minutes.
Stir in the scallions and cilantro and cook for 1 minute. Serve hot.
Interesting Facts
Miso paste is made from fermented soybeans, and is a staple in Japanese cooking.
Mirin is a sweet rice wine used in Japanese cooking.
Sake is a type of rice wine that has a more subtle flavor than mirin.
Scallions and cilantro are both popular garnishes for miso soup.