Bring a pot of water to a boil. Add the onion and ribs. Boil for 1 hour or for longer, if needed, until the meat is tender. Drain and pat dry.
In a small bowl, mix together the tamarind, garlic, mirin, rice vinegar, miso, soy, honey, chilli sauce and sesame seeds.
Preheat an outdoor grill or chargrill pan. Brush the meat with the oil and season well with sea salt and black pepper. Grill on low direct heat until the edges start to crisp and the meat begins to brown. Start to brush the marinade on and then turn over after 5 minutes. Keep brushing until everything is sticky and golden.
Serve the ribs with a sprinkle of chopped coriander and green chilli and extra marinade to dip into.