In small bowl, stir together yogurt, garlic, onion, vinegar, oil, oregano, salt and pepper. Cover dressing and refrigerate for 15 minutes or up to 1 day.
Kabobs: Cut each cucumber into 6 pieces. Cut each pepper into 8 chunks.
On eight 8-inch (20 cm) bamboo or metal skewers, thread 1 piece each of cucumber, pepper and tomato; repeat twice.
Brush each kabob liberally with dressing; place on lettuce-lined platter or individual plates. Sprinkle with feta. Serve with remaining dressing.
Tip: Set out small bowls of prepared vegetables and have kids make their own kabob combination.