Cut peppers in half lengthwise, remove seeds, place skin side up on a baking sheet. Roast under heated oven broiler for 8-10 min until skin blisters black. Remove, cover with a wet kitchen towel for 10 min. Now remove the skin, finely grind the flesh with oil and balsamic vinegar in a blitz chopper, season with salt and season with pepper. Leave to cool for 1 hour.
For the gazpacho, roughly chop the garlic. Peel cucumber, cut in half lengthwise and scrape out seeds with a teaspoon. Cut cucumber into coarse pieces. Pluck sorrel leaves, rinse and spin dry.
Blend cucumber, garlic, sorrel, olive oil, balsamic vinegar, mustard and crème fraîche in a blender until very fine. Season with salt, cayenne pepper and juice of one lemon. Leave to cool for 1 hour.
For the crab tails, cut the garlic into thin slices. Heat 2 tbsp oil in a frying pan. Add the garlic and cook the king prawns in it over medium heat for 1 minute on each side. Season with salt and pepper. Cool the crab tails a little. Cut crab tails in half lengthwise and place on a flat plate. Drizzle with juice of one lemon and remaining oil. Cover with plastic wrap and marinate for 30 minutes.
Fill cold sorrel gazpacho into glasses. Pour the bell pepper puree on top. Evenly distribute crab tails on top and bring to the table on the spot.