Fresh mint, pistachios, and lemon juice bring Middle Eastern flavors to lamb. Serve with creamy Flageolet beans for a well-rounded and filling meal.
Preheat oven to 350 degrees. Place mint, parsley, pistachios, garlic, and lemon juice in the bowl of a food processor fitted with the metal blade. Pulse to combine. With machine running, add 1/2 cup olive oil through the feed tube; process until smooth. Season with salt and pepper.
Lay lamb flat on a clean work surface. Spread mint mixture evenly over lamb, leaving a 1-inch border all around. Starting at the narrow end, roll lamb into a tight log; tie well with kitchen twine.
Heat remaining tablespoon olive oil in a cast-iron skillet over medium heat. Place lamb in pan, and cook until browned on all sides, 7 to 10 minutes. Place in oven; roast until meat thermometer registers 140 degrees when inserted in the center, about 1 hour 10 minutes. Transfer lamb to a platter or cutting board, and let rest 15 minutes.
Meanwhile, make pan sauce: Pour off fat from skillet. Add stock, and deglaze pan by scraping up any browned bits with a wooden spoon. Simmer until liquid is slightly thickened, about 5 minutes. Remove from heat, and serve with stuffed lamb.