Put the gin, vermouth, half the lemon zest and juice, the olive brine, sugar and olive oil in a bowl, whisk to combine, then season. Taste and add a splash more brine or lemon juice if needed. Stir in the prawns and chill for 20 mins to marinate. Lightly crush the olives to break them using the back of a knife, and set aside.

Arrange the chicory and lettuce leaves between six plates or bowls. Scatter over the chillies and parsley, then spoon over the prawns along with the marinade. Sprinkle over the olives, remaining lemon zest and some black pepper to serve.