Step 1) In a small mixing bowl, combine parsley, mint, oil, lemon juice, garlic , crushed red pepper, 1 1/2 teaspoon of salt and 1 teaspoon black pepper. This is your chimichurri.
Step 2) Season the lamb with remaining salt and black pepper. Rub half of the chimichurri over the lamb. Marinate for 6 hours or up to 24 hours.
Step 3) Preheat oven to 400°F. Remove lamb from refrigerator and wipe off excess marinade. Place the lamb in a roasting pan.
Step 4) Roast the lamb in the upper third of the oven, for 50 to 60 minutes or until a thermometer inserted in the thickest part of the roast registers 145°F for medium-rare. Transfer the roast to a carving board and let rest for 10 minutes.
Step 5) Serve with the remaining chimichurri on the side.