1.Shell and devein prawns, leaving tails intact. Combine prawns, basil, garlic and rind in large bowl. Cover; refrigerate 3 hours or overnight.
2.Cook prawns on heated oiled barbecue (or grill or grill plate), uncovered, until changed in colour and just cooked through.
3.Meanwhile, make avocado mash. Mash flesh of one avocado in small bowl until almost smooth. Coarsely chop flesh of remaining avocado; add to bowl of mashed avocado with remaining ingredients; mix well.
4.Serve prawns with avocado mash and lime wedges, if desired.