In a bowl that will take the crabmeat later, whisk together the mirin, wasabi, rice vinegar, sesame oil and salt. Then remove around 4 teaspoons to another big bowl that will fit your salad in later.
To the first, more generous amount of dressing, add the finely chopped chile and then the crabmeat, and fork through to mix thoroughly.
To the small amount of dressing in the other bowl, add the lime juice and then the salad leaves and toss well to mix before arranging on 4 plates.
Spoon a quarter of the mixture into a regular metal kitchen third-cup measure, squishing down to get it all in, then take it over to a salad-lined plate and unmold in the center of it. Just turn over, tap and the crabmeat should fall out. Continue with the remaining 3/4 of the crabmeat and the 3 other plates.
Using a rounded half spoon measure, scoop out curls or humps of avocado and dot around on top of the salady bits. Spritz with a little lime juice.
Sprinkle the chopped chives over the 4 mounds of crab and take the plates to the table.