Preheat a lightly greased barbecue flat plate to high. For dressing, combine makrut lime leaves, nam prik pao, lime juice, fish sauce, sugar and oil in a bowl. Stir in lemongrass and coriander; season to taste.
Halve lobster lengthways, remove vein that runs down the back of lobster and drizzle with oil. Place cut-side down on flat plate and cook until just cooked and lightly browned (10-12 minutes).
To serve, transfer lobster to a serving platter. Drizzle with sauce. Top with chilli, spring onion, crisp shallots and garlic. Serve with lime cheeks.
