Mix kosher salt, black pepper, and garlic powder in a small bowl. Use this mixture to season all sides of the ribeye steak generously. You can also substitute your favorite steak seasoning. After applying seasoning, let the steak rest at room temperature for about 45 minutes.
Prepare 2 temperature zones on your grill. This can be one hot side and one unheated side on the main cooking grate. Alternatively you can heat the full main grate and utilize your warming rack. I heat one side to ~500 degrees F for searing, and leave the burners off on the other side.
Sear the steak over the hot side of the grill for 5 minutes on each side. Halfway through each side (so after 2.5 minutes), rotate the steak 45-90 degrees to form grill marks on the steak.
After the tomahawk steak has seared for 5 minutes on each side (10 minutes total), move the steak to a raised warming rack or to the cooler side of the grill.
Stick your probe meat thermometer into the very center of the cut to measure internal temperature.
Place butter stick, garlic cloves, olive oil, and thyme in the aluminum pan. Then place the aluminum pan under the steak, if possible, to catch drippings. After a few minutes, the steak drippings and ingredients will mix together.
Baste the steak with the aluminum pan mixture every 10 minutes until the tomahawk steak reaches your desired doneness.
Once the steak reaches its desired doneness, remove from the grill and place on a cutting board or serving dish. The steak should rest for 10-15 minutes before cutting/serving. Enjoy!