Place stock, coconut milk, fish sauce, caster sugar, ginger, lime leaves, lemongrass, and chilli in a large pot over medium-high heat. Gently simmer for 10 minutes. Remove from heat.
Add lobster and lime juice.
Allow to sit for 10 minutes or longer for the flavours to infuse.
Remove the broth from the fridge half an hour before serving.
To assemble: spoon broth and lobster into individual bowls, and top with delicate herb salad ingredients.