Place the shrimp in a steam basket set over boiling water, cover and cook for about 4 to 5 minutes, until the crustaceans turn pink and completely opaque.
Immediately transfer them to a bowl and throw in one or two dozen ice cubes. Stir things around a bit so the ice starts melting and set aside, stirring every now and then until the shrimp is completely cooled.
Meanwhile, supreme your grapefruit and then cut it into bite size chunks; place the pieces of fruit in a large mixing bowl and save the juice for another use.
Once completely chilled, drain the shrimp really well and add it to the bowl with the grapefruit, followed with the rest of the ingredients.
Toss delicately until well combined and serve immediately.
This salad will keep for up to a full day in the refrigerator, so you could make it in advance if you wanted to. However, the avocado may have a tendency to brown a little bit, so make sure you add it at the very last minute.