Combine butter, parsley, chili flakes, diced chilli, garlic, lemon zest, rosemary, salt, and pepper in a bowl; set aside.
Using a sharp cook’s knife, split lobster tail in half lengthwise through the middle of the tail. Transfer lobster halves, shell side down, to a baking sheet;
Heat a charcoal grill, once the coals have gone white and the flames have died downPlace lobster halves, flesh side down, part of grill; cook until slightly charred, 2-3 minutes. Flip lobster over and using a spoon, spread lobster with the butter; continue grilling until lobster meat is tender, 3-5 minutes more. Remove from the grill and spoon over a little extra butter mix on each