Blend chopped onions, crushed garlic, lemon juice, salt, cumin, and olive oil in a blender and puree.
Coat the lamb pieces with marinade and cover with plastic bag and keep in the refrigerator overnight
Prepare the grill about 30 minutes before grilling and preheat the broiler about 5 minutes and then arrange the kebab pieces and broil till cooked and remove from fire
Arrange either with the skewer or separately on a flat serving dish with yogurt and bread or with white rice and spicy sauce