Place lobster tails on a baking sheet lined with foil. With a sharp knife or kitchen shears, carefully cut top side of lobster shells lengthwise. Pull apart shells slightly. Make a slit in the middle of the lobster meat and season meat with equal amounts butter, garlic salt, and pepper.
Broil lobster tails until lightly browned and lobster meat is opaque, about 15 - 20 mins. Keep an eye on them while they're in the oven so they don't burn.