In a large pot, bring 3 litres of water to the boil, add a tablespoon of lemon juice, then drop the whole tiger prawns into the pot. As soon as the prawns rise to the surface they’re ready, so use a slotted spoon to scoop them out and drop them in a bowl of iced water. Leave them for a couple of minutes so they stop cooking, then drain them.
Carefully remove all the shells of 8 prawns, taking care not to damage them, by first removing the heads, then legs, then body of the shell, and tails of all but 4 prawns. If you wish to de-vein the prawns, use a toothpick or tweezers to tug out the poop; don’t slice the prawns down their backs. If messy from the juices from the heads, rinse the prawns quickly under cold running water, pat them dry, put them in a clean bowl, and refrigerate them.
In a small bowl, make the seafood sauce by stirring the mayonnaise and tomato sauce (ketchup) until combined, then add the lemon juice, finely diced purple shallot, spices and seasoning, and finely sliced chives and spring onions/scallions, and finely chopped fresh dill, stir until well-combined, then refrigerate.
Wash the lettuce leaves, pat them dry, then arrange the leaves in cocktail glasses or glass bowls, so they line the bowl and prettily protrude over the edges.
Finely slice or shred the remaining lettuce leaves, transfer to a bowl, and combine with half the seafood sauce. Scoop this out with a spoon and divide between the cocktail glasses or bowls so that it almost fills them.
Chop all of the prawns, except the 4 prawns with tails, into large chunky pieces, combine with the remaining seafood sauce, and pile them onto the salad. Arrange the last 2 prawns with tails attractively on top of them, then sprinkle on fresh dill sprigs and serve immediately with quarters of limes or lemons.