Bring a large pan of water to the boil and tip in both packets of prawns. Cook for around 3-4 minutes, until pink and cooked through. Drain the prawns once cooked and spread out on a plate to cool.
Meanwhile, mix together the mayonnaise, ketchup, Worcestershire sauce, lemon juice and paprika in a bowl. Taste and season with salt and pepper.
Once the prawns are cool to the touch, mix with the sauce. Line 6 cocktail glasses with avocado slices around the sides and divide the shredded lettuce between them. Top with the prawn cocktail mixture and sprinkle with a little cayenne pepper. Serve immediately.
