In a small bowl, mix the Moroccan seasoning, salt, sugar, and oregano. Rub onto the lamb, coating it evenly. Place the lamb in a deep bowl; pour in the beer. Let marinate at least 20 minutes.
Heat your grill to medium and prepare it for indirect grilling. Grill the lamb over indirect heat, turning it occasionally, until it's cooked to your liking (20-30 minutes for medium rare). Heat the tortillas on the top rack for a few seconds, or until they're slightly toasted but still pliable.
Transfer the lamb to a cutting board and let rest 10 minutes. Meanwhile, prepare the cucumber salsa by mixing the onion, cucumber, cilantro, lime juice, and a pinch of salt.
Slice the lamb thinly across the grain.
Serve the lamb in the warmed tortillas with Greek yogurt, cucumber salsa, and radishes. Squeeze the lime wedges over the lamb, if desired.