1. lay langoustines on a surface and, using a large, sharp knife, cut in half lengthwise from the head towards the tail. Rinse the innards present in the head part under cold running water. (Remove any black intestines from the tail section using a sharp knife. Place langoustines on a kitchen towel to drain. Finely dice garlic cloves.
2. Heat 4 tbsp. olive oil in a large frying pan and roast 18 half langoustines, cut side down, with half the garlic and lemon zest for 1 minute over medium heat. Turn langoustines to other side and roast repeatedly for 1 minute. Season with salt and pepper; keep warm. Cook remaining langoustines in same manner.
Serve with terrine and bell pepper vinaigrette.