Cut stems out from a cilantro bunch and chop into 1/4-inch pieces.
Cut the galangal into thin slices.
Place garlic cloves, black pepper, salt, MSG, palm sugar, galangal, and cilantro into the mortar and pound with the pestle until you turn the ingredients into a paste, then move the paste to a mixing bowl.
Add soy sauce, oyster sauce, and honey to the bowl and mix everything together. You've got your marinade!
Wash the chicken legs and pat them dry with paper towels to remove excess moisture.
Place chicken legs into a dish where you will marinate them, cover with the marinade, and mix thoroughly to ensure that the sauce smothers the chicken legs completely.
Allow the chicken to marinate for at least 1 hour.
Preheat on low, and brush the grill with cooking oil or olive oil.
Place the chicken legs onto the grill with the skin side up.
Depending on your grill's heat output, you may or may not want to close the lid. If the heat yield is low or normal, go ahead and close the lid. But if the grill produces a higher temperature than normal, you may want to close the lid periodically — doing so will speed up the cooking process and put out any grease fires on the grill as you starve the fire of oxygen. However, keeping the lid closed for too long on a grill that gives off lots of heat will cause your chicken legs to dry out and possibly get charred.
Baste the chicken legs with a single layer of the marinade sauce.
Turn the chicken legs onto the skin side after the first 10 minutes, then flip them back 2 minutes later (so the skin doesn't burn). Continue flipping the legs at the same interval and baste the legs a couple of times more between flips. For best results, adjust the number of flips based on the heat output of your grill.
Continue to cook until the meat has reached temperatures of 165°F or higher before serving the chicken legs (ensure you have a meat thermometer handy when you grill). The cooking time will vary depending on the size of the legs and the grill's heat output.