Heat the barbecue to 350°F. Plunge the lobsters headfirst into boiling water. Using tongs, remove them from the water as soon as it starts boiling again, or after 3 to 5 minutes of cooking. Cut the shell lengthwise. Generously brush with garlic butter. Cook on the barbecue grill, shell side up, for about 10 minutes. Brush with garlic butter once or twice during cooking to prevent drying out. Flip and continue cooking for 5 minutes or until the flesh is firm. Serve with rice, melted garlic butter, and a green salad.