In a large, shallow non-metallic baking dish, combine marinade ingredients, stirring until well blended and creamy. Add lamb cubes and stir around until well coated. Cover and refrigerate 6 yours or overnight, stirring occasionally.|
Position barbecue rack about 5 inches above preheated coals. Thread lamb cubes onto metal skewers, leaving a small space between cubes so meat cooks evenly. Thread onion pieces, cherry tomatoes, and pepper squares onto separate skewers, brush with some remaining marinade.
Arrange lamb skewers over center of coals and cook turning and basting with marinade occasionally, 17-20 minutes. Halfway through cooking time, add vegetable skewers to barbecue and cook, turning and basting with marinade, 8-10 minutes.
Arrange skewers on long serving platter and surround with fresh sprigs of rosemary. Serve with rice, salads, or other accompaniments.