For the lamb: trim all fat from the lamb and cut into 2-inch cubes. Combine remaining marinade ingredients in a large resealable plastic bag and mix well.

Add the lamb cubes to the bag, tossing to coat. Seal bag and marinate in the refrigerator at least 2 hours, preferably overnight, rotating the bag occasionally to continually coat the lamb.

Preheat an outdoor grill to medium heat. Remove lamb from refrigerator about 30 minutes before grilling to bring the meat to room temperature.

To assemble the kabobs: fill skewers, alternating peppers, lamb, tomatoes, onions and mushrooms until all ingredients are used.

Grill skewers, rotating to char lamb on all sides, until cooked to desired doneness, about 7 to 8 minutes for medium-rare.