Stir together the dried rosemary, dried oregano, garlic powder, salt, smoked paprika and black pepper in a small bowl. Set aside.
Rub olive oil all over the leg of lamb on both sides. Coat with the spice mixture on both sides as well.
Place the lamb on the smoker. Insert a leave-in meat thermometer in the center of the lamb. Close the lid and smoke until it reaches your desired internal temperature.
Remove the lamb from the smoker. Cover with aluminum foil and let the meat rest for 15-20 minutes to allow the juices to redistribute to the meat. Carve into thin slices.