Melt butter in a small pan. Add fresh lemon juice, parsley and sea salt.
Heat grill to high heat (450 degrees). Place prawns directly over the heat, shell side down. Baste flesh with butter. Grill for 4-5 minutes, leaving the cover up.
Turn prawns over and continue grilling another 3-4 minutes or until prawns turn opaque. Baste with more butter and serve.