It's best to make this dressing just before using, because it darkens on standing. If it must be made in advance, spread with a thin film of mayonnaise, (this will minimize discoloration) then cover and refrigerate until needed. Stir mayonnaise in before serving.
Scoop flesh from avocados and press through a fine sieve; beat in remaining ingredients. Serve over wedges of lettuce, halved endive spears, or in hollowed out tomatoes. Or use to dress any seafood salad instead of mayonnaise.