1. Adjust an oven rack to the upper-middle position so it is 4 inches from the broiler element. Heat the broiler to high and line a rimmed baking sheet with aluminum foil.

2. In a small dish, mix together 2 tablespoons of the kosher salt and the pepper. Set the lamb on a cutting board and rub both sides with the chopped garlic, then season both sides with the salt-and-pepper mixture. Drizzle both sides of the lamb with 1 tablespoon of the grapeseed oil and transfer the lamb to the prepared baking sheet.

3. Broil until browned, 6 to 8 minutes. Turn the lamb over and brown the other side until the lamb is cooked to your liking, 6 to 8 minutes more for medium-rare (125° to 130° on an instant-read thermometer). Take the lamb out of the oven and set aside to rest for 15 minutes. Transfer to a cutting board (reserve any accumulated juices on the pan) and slice crosswise (against the grain) into thin pieces. Place on a serving platter and sprinkle with the cilantro.

4. In a medium skillet, add the remaining 2 tablespoons of the oil, sliced garlic, crushed coriander seeds, mustard seeds, cumin seeds and red pepper flakes. Set the heat to medium and cook, stirring occasionally, until the mustard seeds pop and the garlic is golden, about 1½ to 2 minutes. Add the remaining ½ teaspoon of salt, pour the seasoned oil over the sliced lamb and serve.