Heat the grill to its highest setting. Peel and crush the garlic and halve, deseed and very finely chop the chilli. Coarsely chop the coriander leaves and juice the lemon. Put half the olive oil in a small saucepan, add the crushed dried chillies and garlic and gently warm over a low heat for 2–3 minutes, then remove from the heat and leave to infuse while you prepare the langoustines for grilling (see footnote). Pour the cool, infused oil into a large bowl, add the langoustines and toss to coat. Place the langoustines shell side down on a lipped baking tray, season with salt and a little pepper and grill for 3–5 minutes, depending on size. Halfway though cooking, baste the langoustines with any remaining infused oil from the bowl. Meanwhile, add 1 tablespoon lemon juice to the remaining olive oil with the chopped chilli, coriander and some salt and pepper. Once cooked, the langoustine tail meat will have turned opaque and will be starting to shrink a little from the shell. While still hot, drizzle over the dressing. Serve immediately.