Peel the avocado and cut into small squares
Cut a 10 cm chunk off the cucumber and peel. Cut into strips with a potato peeler.
Toss the avocado and cucumber in the lemon juice.
Shred the little gem lettuce and mix with the cucumber and avocado
Place on a plate or in a cocktail dish, leaving enough room to top with the prawns.
Add the mayonnaise to a bowl.
Add the ketchup, Worcestershire sauce, Tabasco and lemon juice and mix well.
Add the prawns and stir gently until well coated
Top the lettuce with the prawn mixture.