How to Make It
On a baking sheet, lay out the lamb. In a small bowl, whisk the yogurt with the oil, garlic, cumin, crushed red pepper, black pepper, salt and 1/4 cup of the orange juice and rub all over the lamb. Wrap in plastic and refrigerate overnight.
Preheat the oven to 450°. Lay the lamb on a rack set over a baking sheet and let stand for 30 minutes. Roast for 30 to 35 minutes, basting occasionally with the remaining 1/4 cup of orange juice, until an instant-read thermometer inserted in the meat registers 130° for medium-rare. Let rest for 15 minutes.
Thinly slice the lamb and serve with corn tortillas, avocado, cilantro and lime.