01 - Preheat oven to 400°F. Line a roasting pan with foil.
02 - Pat lamb dry with paper towels. In a small bowl, mix cumin, paprika, coriander, oregano, salt, pepper, minced garlic, lemon zest, lemon juice, and olive oil to form a thick paste.
03 - Rub the spice paste evenly over entire surface of lamb. Place lamb on a rack in the prepared roasting pan.
04 - Roast at 400°F for 15 minutes to develop a flavorful crust.
05 - Reduce heat to 325°F and continue roasting for 1 hour 45 minutes, or until internal temperature reaches 135°F for medium-rare.
06 - Remove lamb from oven, tent loosely with foil, and let rest for 20 minutes before slicing thinly against the grain.
07 - While lamb rests, combine Greek yogurt, lime juice, mint, garlic, salt, and pepper in a bowl. Mix thoroughly and set aside.
08 - Heat corn tortillas in a dry skillet over medium heat for 30 seconds per side, or wrap in foil and warm in oven for 5 minutes.
09 - Fill each tortilla with sliced lamb. Top with onion, cilantro, feta or queso fresco, lettuce or cabbage, and jalapeño if desired. Drizzle with yogurt-lime sauce and serve with lime wedges.