01 - Preheat oven to 400°F. Line a roasting pan with foil.
02 - Pat lamb dry with paper towels. Mix cumin, paprika, coriander, oregano, salt, pepper, minced garlic, lemon zest, lemon juice, and olive oil in a small bowl to create a thick paste.
03 - Rub spice paste evenly over entire surface of lamb. Place seasoned lamb on rack in prepared roasting pan.
04 - Roast at 400°F for 15 minutes to develop crust.
05 - Reduce oven temperature to 325°F. Continue roasting for 1 hour 45 minutes, until internal temperature reaches 135°F for medium-rare.
06 - Remove lamb from oven and tent loosely with foil. Let rest for 20 minutes before slicing thinly against the grain.
07 - Combine Greek yogurt, lime juice, chopped mint, minced garlic, salt, and pepper in a bowl. Mix thoroughly until smooth 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 warm tortilla with sliced cumin-crusted lamb. Top with red onion, cilantro, feta or queso fresco, lettuce or cabbage, and jalapeño if desired. Drizzle with yogurt-lime sauce and serve with lime wedges.