Heat the oil in a frying pan and gently fry the shallot for five minutes, or until softened. Add the garlic, pork belly, chilli, fish sauce and cook for five minutes. Add 300ml/10fl oz water and simmer for 40 minutes to one hour.
Meanwhile in a separate saucepan make the caramel by heating the sugar and 1 tbsp water until the sugar melts and the caramel is golden-brown. Pour this caramel over the pork belly and cook for a further 5-10 minutes.
For the carrot salad, heat the sugar, vinegar and fish sauce in a saucepan until the sugar melts and the mixture boils. Stir in the grated carrot, then remove the pan from the heat and set aside to cool.
Assemble the sandwich by slicing the baguette in half lengthways. Spread with the mayonnaise and add the salad, coriander and pork belly. Cut the baguette into four sandwiches and serve with the carrot salad.