Blend the onion, green chiles, garlic, and lime juice together in a food processor until smooth; add the cilantro and pulse until the cilantro is finely chopped into the mixture.
Bring the chicken stock to a boil in a saucepan. Stir the cilantro mixture, salt, butter, and rice into the water and return to a boil; After boiling is returned cook for 1 minute. Cover and rest for 5 - 10 minutes. Fluff with a fork.