Add the garlic, herbs, lemon juice and zest to a small bowl. Slowly add 3 tablespoons olive oil, season with salt and pepper, and stir until combined. Coat the lamb on all sides with half of the herb mixture.
Prepare a grill to medium-high heat. Put the lamb on the grill and grill for approximately 5 minutes per side. Remove from the grill.
Preheat the oven to 350°F.
Coat the lamb on all sides with the remaining herb mixture.
Put the lamb in a large cast-iron skillet. Drizzle 1 tablespoon olive oil over the lamb. Place the skillet in the oven and cook for 30 minutes, or until the meat is cooked through or desired doneness. Remove from the oven.
Transfer to a serving plate. Serve immediately.