1. Heat a heavy-based saucepan over a medium heat and add the sugar and 2 tablespoons of water. Gently stir, then leave to simmer for 4-5 minutes, or until the sugar has dissolved and the mixture is light golden brown. Remove from the heat and set aside.
2. In a bowl, combine the pork, shallot, spring onions, lemongrass, garlic, fish sauce, salt and pepper and pour in the caramel sauce. Mix well and place in the fridge for 30 minutes to marinate.
3. Soak four bamboo skewers in water for 15 minutes to stop them burning once on the grill. Preheat a barbecue or cast-iron griddle pan to a medium heat. Thread the pork onto the skewers and cook for 10 minutes, until caramelised. Add a little oil if it starts to stick.
4. Lightly toast the baguettes on the grill, then split them lengthwise and spread with a thin layer of mayonnaise and pate. Release the grilled pork from the skewers into the baguettes. Top with the cucumber, coriander leaves and fresh chilli to serve.