Remove the ribeye steaks from the refrigerator and let them sit at room temperature for about 30-40 minutes before grilling.
Preheat the grill to high heat. Place a cast iron skillet on the grill to preheat for about 10-15 minutes.
Rub each steak on both sides with avocado oil. Mix the kosher salt, freshly ground black pepper, minced garlic, rosemary, and thyme together in a small bowl. Season both sides of the steaks evenly with this mixture.
Once the grill and skillet are hot, place the seasoned steaks in the skillet. Let them cook without moving for about 4-6 minutes on one side, depending on the desired level of doneness.
Flip the steaks over, add the unsalted butter to the skillet, and cook for another 4-6 minutes for medium-rare to medium. Baste the steaks with the melted butter in the skillet as they cook.
Remove the steaks from the skillet and let them rest on a cutting board or plate for at least 5 minutes before slicing to allow the juices to redistribute throughout the meat.
After resting, slice the steaks against the grain and serve immediately.