Prepare the Prawns:
Shell the prawns leaving the tail tip intact - then de-vein the prawns.
Heat a little oil in a pan and quickly sear the prawns, grinding over with salt and pepper as they cook. This should only take a minute or two at the most. Remove from the pan and set aside to cool.
Make the sauce:
In a small bowl add the mayonnaise, Worcestershire sauce, lime juice & tomato ketchup/paste. Mix and then season to taste with salt and finely ground pepper.
Cover and keep in the fridge until you are ready to use it.
Assemble the dish:
Keep two prawns aside to garnish the top of the dish. Slice the remaining prawns into a small dice.
Take two martini glasses.
Place some shredded cos lettuce at the base of the glass then top with half the diced avocado. Sprinkle over the diced prawns then spoon over with a little of the sauce. Repeat with another layer of lettuce and avocado then top with a whole prawn. Serve the extra sauce on the side.