For the lamb, put the carrot, onion, star anise, garlic, parsley and chipotle chilli into a large saucepan. Half-fill the pan with cold water, then lay the lamb belly on top and pour over just enough water to cover the meat. Bring the mixture to the boil, then reduce the heat until simmering and simmer for 1 hour, until the meat is really tender.
Meanwhile, for the pickled red onions, put the sliced red onions into a bowl, then heat the cider vinegar, caster sugar, mustard seeds and salt in a non-reactive pan until the sugar has dissolved and the mixture is just simmering.
Pour the liquid over the onions, then add the cucumber, stir well and set aside to cool.
For the barbecue sauce, heat a non-reactive frying pan over a medium heat until hot, then add the chipotle paste and stir-fry for a 1-2 minutes. Add the ketchup and maple syrup and stir-fry for a further 2-3 minutes, or until bubbling. Add the Worcestershire sauce, cider vinegar and soy sauce, bring the mixture to the boil, then reduce the heat until simmering and simmer for 5-6 minutes, or until thickened. Set aside.
When the lamb has cooked, remove it from the pan using a slotted spoon and set aside to drain and cool.
Preheat the oven to 200C/180C Fan/400F/Gas 6. Warm the naan bread or pide in the oven for a few minutes.
To serve, coarsely shred the lamb meat and fold the meat into the warm barbecue sauce. Spoon the mixture on top of the warmed bread, with some of the pickled red onions and coriander leaves scattered on top.