Preheat oven's broiler.
Rinse langoustine and pat dry. Pierce each langoustine with toothpicks through body and head. Lay on an oiled baking sheet.
Combine butter, lemon zest, dill and breadcrumbs. Season with salt and red pepper flakes. Spread onto langoustine and broil for 2-3 minutes.
Remove from oven, remove toothpicks and serve.