Combine all the ingredients, except for the chicken, in a large glass measuring cup or mixing bowl and stir vigorously until well combined.
Place the chicken thighs in a single layer in a non-reactive container such as a glass or porcelain baking dish and pour in the marinade; toss the chicken thighs around until they are completely coated. Make sure that the marinade makes it all the way to the bottom of the dish. Cover with a piece of plastic film and place in the refrigerator to marinate for at least 4 hours, but preferably overnight.
When you are ready to grill your chicken, preheat a grill to high heat and brush the grills with a little bit of oil, if necessary.
Once the grill is super hot, place the chicken on the grill, nice looking side down; Close the lid and cook for about 5 minutes, or until the meat easily detaches from the grill, then flip the chicken thighs.
Spoon a little bit of the leftover marinade over each thigh, close the lid and let the meat cook for another 3 to 5 minutes, or until the chicken is nicely charred, cooked all the way through and its juices run clear.
Remove the pieces of chicken to a clean plate and garnish with chopped green onions and toasted sesame seeds before serving, if desired.