Combine the lemon juice, smoked paprika. mayonnaise, and 1.5 tsp smoked salt in a bowl. Cover and chill until serving.
Season prawns with the some salt and some pepper, then set aside. Toss avocado with olive oil and season with sea salt and black pepper. Set aside.
Divide the iceberg lettuce among 8 serving glasses. Top with cucumber, avocado and most of the spring onion. Put the prawns on top and finish with a big dollop of the smoky mayonnaise.
Sprinkle prawns with remaining onion and some smoked paprika and serve. Great for appetizer.