Combine the olive oil, lemon juice, garlic, scallion, and coriander in a mixing bowl and season to taste with 1/2 teaspoon of salt or more; season with cayenne pepper if you wish. Add the lamb and marinate for as long as possible (up to 3 hours at room temperature or 6 hours in the refrigerator); turn the meat in the marinade every now and then. Soak bamboo skewers in water while this marinates.
Position the broiler pan 4 to 5 inches away from the heat source and preheat the broiler. Thread lamb cubes on skewers. Broil kebabs for 6 to 7 minutes a side or until lamb is cooked through.