Prepare outdoor grill with medium-hot coals, or heat gas grill to medium-hot.
Whisk together garlic, lemon juice, lemon peel and oregano in a small bowl. Slowly whisk in olive oil to make marinade.
Thread tomatoes on skewer. On other skewers separately thread mushrooms, green pepper and sliced meat. Brush all threaded skewers with marinade.
Grill green pepper, covered, 2 minutes. Add mushrooms; grill, covered 2 minutes. Add tomato and beef; grill, covered, 3 minutes per side.
Place all skewers on platter. Season with salt and pepper to taste and sprinkle with chopped mint. Serve with lemon wedges.
Servings: 6