Trim fat from lamb, and cut lamb into 24 (2 inch) cubes.
Combine vinegar and next 6 ingredients in a large zip top heavy-duty plastic bag. Add lamb cubes, and marinate in refrigerator 8 hours, turning bag occasionally.
Cut eggplant lengthwise into quarters. Cut each quarter crosswise into 4 pieces. Cut zucchini lengthwise in half. Cut each half crosswise into 4 pieces. Thread 2 eggplant pieces, 1 zucchini piece, and 1 onion wedge onto each of 8 (10 inch) skewers.
Remove lamb from bag, reserving marinade. Thread 3 lamb cubes, 1 red bell pepper piece, 1 yellow bell pepper piece, and 1 mushroom alternately onto each of 8 (10 inch) skewers.
Coat grill rack with cooking spray; place on grill over medium hot coals. Place eggplant kebabs on rack, and cook 15 minutes, basting with reserved marinade. Turn eggplant kebabs, and cook 7 minutes. Add lamb kebabs to rack, and cook 4 minutes on each side or to desired degree of doneness, basting with reserved marinade.
Yield: 8 servings (serving size: 1 eggplant kebab and 1 lamb kebab).