01 - Preheat your oven to 400°F. Line a roasting pan with foil.
02 - Pat the 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 make a thick paste.
03 - Rub the spice paste all over the lamb. Place the lamb on a rack in the prepared roasting pan.
04 - Roast for 15 minutes at 400°F, then reduce heat to 325°F and continue roasting for 1 hour 45 minutes, or until the internal temperature reaches 135°F for medium-rare.
05 - Remove lamb from oven, tent with foil, and let rest for 20 minutes before slicing thinly.
06 - While the lamb rests, combine Greek yogurt, lime juice, mint, garlic, salt, and pepper in a bowl. Mix well and set aside.
07 - Warm the corn tortillas in a dry skillet or wrap in foil and heat in the oven for 5 minutes.
08 - Fill each tortilla with slices of cumin crusted lamb, top with onion, cilantro, feta or queso fresco, lettuce or cabbage, and jalapeño if using. Drizzle with yogurt-lime sauce and serve with lime wedges.