Place the steak on a rimmed plate or baking sheet and rub all over with the smashed garlic cloves. Sprinkle evenly with the rosemary, thyme and lemon zest. Drizzle with the olive oil. Rub the herb mixture into the meat. Allow to sit at room temperature for 30 minutes.
Prepare a grill or grill pan for medium-high heat. Preheat the oven to 500 degrees F. Set a wire rack over a rimmed baking sheet.
Sprinkle the steak evenly on both sides with the salt. Grill until nicely seared all around, about 5 minutes per side. Remove the steak to the wire rack, and transfer to the oven. Cook for an additional 15 minutes, flipping halfway through, or until an instant-read thermometer inserted in the middle of the steak reads 120 degrees F.
Remove the steak to a plate, and squeeze the lemon half over the top. Let rest for 10 minutes before slicing. Finish with a sprinkling of coarse salt.