Take your steak and season it on both sides with kosher salt and black pepper. I have stated this before, if you buy a quality steak, the only seasoning it needs is salt and pepper. Once you have it seasoned on both sides, heat up your grill. Steaks need to come up to room temperature before you grill them. When they are at room temperature, they cook more even, the temperature readings are more concise, and the meat has had a chance to relax and get loose, this makes for better grilling.
Once your grill is hot, place your steak on the grill and grill mark it. The steak will need twice as long as the lobster tail to cook. Lobster needs to be cook at a high heat temperature so that it will get cooked thoroughly because you will leave it in the shell to help protect the meat on the grill. Once you have your steak grill marked and flipped baste it with some melted butter infused with garlic and parsley. This will help keep it moist and tender. After you turn your steak place your lobster on the grill meat side down, and get it grill marked. Lobster cooks pretty fast, and your target temperature is between 135°F-140°F (57°C-60°C), this is the optimal temperature for your lobster. Your steak should be cooked to 135°F (57°C) then pulled from the grill and allowed to rest for at least 5 minutes. The thicker the steak is, the longer it needs to rest to get up to temperature.