Simmer lamb belly with carrot, onion, star anise, garlic, parsley, and chipotle chilli in water for 1 hour.
Heat cider vinegar, sugar, mustard seeds, and salt until sugar dissolves to create pickling liquid.
Pour liquid over sliced onions and cucumber and leave to cool.
Stir-fry chipotle paste, ketchup, and maple syrup, then simmer with Worcestershire sauce, vinegar, and soy sauce until thickened.
Drain the cooked lamb from the pan and allow it to cool.
Preheat the oven to 200°C and warm the bread for a few minutes.
Shred the lamb, mix with barbecue sauce, and serve on warm bread with pickled onions and coriander.