1. Prepare outdoor grill with medium-hot coals, or heat gas grill to medium-hot (to broil, see below).
2. Whisk together garlic, lemon juice, lemon rind and oregano in a small bowl. Slowly whisk in olive oil to make marinade.
3. Thread tomatoes on metal skewer. On other skewers separately thread mushrooms, green pepper and sliced meat. Brush all skewers with marinade.
4. Grill green pepper, covered, 2 minutes. Add mushrooms; grill, covered, 2 minutes. Add tomato and beef; grill, covered, 3 minutes per side.
5. Place all skewers on platter. Season with salt and pepper. If desired, garnish with fresh mint and lemon wedges.To Broil:
6. Heat broiler. Grease broiler-pan rack. Broil in same order and for same length of time as grilling above.