With a small, sharp knife, make a cut along the back of each prawn and remove the vein, then cover the prawns and refrigerate until ready to serve. Combine the mayonnaise, tomato sauce, horseradish, brandy, chipotle Tabasco, Worcestershire sauce and lemon juice, adjusting to taste. Combine the lettuce and onion in a bowl, then divide among 4 serving glasses, filling to three-quarters full and topping with avocado pieces as you go. Combine the prawns with half the sauce and place evenly on each portion of lettuce. Sprinkle with lemon zest and cayenne pepper, and serve with a lemon wedge on the side. SIMON SAYS Keep the remaining sauce in the fridge for another use. It makes a great dipping sauce for fish ’n’ chips, and is an ideal dressing for pasta salad or potato salad.