For the lemon and pepper butter, simply mix the butter, black pepper and the lemon zest with a pinch of sea salt and set aside.
Heat a grill to high. Combine the langoustines and wine or water in a pan. Bring to the boil, cover, then lower the heat and simmer for 5 minutes. Remove and cool slightly.
Place your langoustines, belly-side down, on a chopping board and cut in half lengthways, discarding the black vein in the tail.
Place, flesh-side up, on a baking tray, top with the lemon butter, sprinkle over the breadcrumbs and drizzle with oil.
Finely grate the zest from 1 lemon into a bowl and set aside, then halve both lemons. Place the lemon halves on the tray. Grill for 5 to 10 minutes, or until golden – keep an eye on it.
Serve the langoustines sprinkled with zest and with the grilled lemon.