Lighter prawn cocktail with avocado

Name: Lighter prawn cocktail with avocado
Ingredients: 500g/1lb 2oz frozen Atlantic prawns, de-frosted, drained; 150ml/5fl oz ready-made gazpacho; 150ml/5fl oz low-fat crème fraîche; 1 shallot, peeled, very finely diced; 2 tomatoes, skins removed, flesh diced; 1 red chilli, stalk removed, finely diced; 6 radishes, trimmed, finely sliced; small bunch fresh coriander leaves, chopped, plus extra sprigs to garnish; 1 lime, juice and zest; 8 dashes Tabasco; salt and freshly ground black pepper; 2 small baby gem lettuces, shredded; 1 large ripe avocado, peeled, stone removed, flesh sliced lengthways; 4 pinches cayenne pepper; 4 large fresh cooked prawns, heads and shells intact; 4 sprigs fresh coriander