Pound the chicken thighs with a meat hammer to even out the thickness and tenderize them.
In a large mixing bowl, mix all the marinade ingredients until well blended. Add the chicken to the marinade and toss well to coat evenly.
Preheat the oven to broil. Adjust the oven rack to about 5-6 inches below the heat source. Place the miso-marinated chicken on a greased rack over a baking sheet. Broil for 3-5 minutes or until the edges are slightly charred, watching carefully to avoid burning the chicken as miso can burn easily.
Take the baking sheet out, flip the chicken thighs, and broil for another 3-5 minutes or until fully cooked.
Cut the chicken into 1/2-inch bite-sized strips for easy serving with chopsticks. Garnish with chopped green onion and toasted sesame seeds. Serve over steamed rice.