For the sauce: in a large bowl mix together the ricotta,yogurt and ketchup. Whisk in the Tabasco, Worcestershire, sprinkle with lemon zest and season with salt and pepper to taste.
Chop the salmon and prawns into bits, reserving 4 prawns to decorate later. Finely cube the cucumber and chop into strips the baby gem lettuce.
Fold all the ingredients into the sauce and mix everything together. Then chill in the fridge for 15 min.
Spoon the salmon and prawn cocktail into 4 martini glasses and decorate each one with a king prawn and a baby gem lettuce leave. sprinkle with extra black pepper and serve.