1. Stir together vinegar, lemon juice, oil, rosemary, salt and pepper. Reserve 1/3 cup, then combine meat with remaining mixture and marinate in fridge for 1 to 4 hrs.
2. Heat grill to medium high. Discard marinade and thread meat onto skewers; thread zucchini and tomatoes onto separate skewers and brush with reserved sauce. Grill kabobs until meat is cooked, about 10 min for medium-rare or 12 min for medium. Cook zucchini until just tender, about 10 min, and grill tomatoes until just soft and skin is cracking, 2 min.
3. Brush meat and vegetables with more of the reserved reserved sauce and serve with flatbread. Makes 6 servings.