To make the Coconut Lime Dressing, whisk the ingredients together in a bowl.
Taste for seasoning and adjust if necessary.
Refrigerate in a sealed container until ready to use.
Fill a stockpot large enough to fit the crabs with water and bring to a boil. When the water reaches a rolling boil, add the crabs and cook for 6 minutes (10 minutes if using mudcrabs).
Remove the crabs from the water and immediately plunge them into icy-cold water to prevent further cooking.
Remove the flesh from the crabs and discard the shells (or reserve them to make a crab stock for later use). Ensure that the crab meat is free of any hard membrane and shell.
In a large bowl, mix together the crab meat, coconut, spring onion, chilli, ginger, cucumber, mints, coriander, red shallots and lime leaves.
Pour in the dressing and allow to stand for 3 minutes only, just long enough for the flavours to mingle.
Dry the mitsuba leaves thoroughly.
Toss the leaves in the dressed crab and mix carefully. If desired, arrange betel leaves or a round of banana leaf on each serving plate.
Pile the salad onto the plates and sprinkle over the fried shallot slices.