Preheat barbecue for medium-high heat. In a blender or food processor, blend yoghurt, basil, chives, parsley, 2 tbs oil, lemon zest and 1 tbs lemon juice until smooth. Season with salt, pepper and more lemon juice, if necessary. Cover the dressing and refrigerate.
Coat chicken with 1 tbs oil and sprinkle with salt and pepper. Barbecue chicken, rotating as needed, for 4 mins each side or until chicken is cooked through. Transfer chicken to chopping board and set aside for 5 mins to rest. Slice chicken.
Meanwhile, toss corn with remaining 1 tbs oil and sprinkle with salt and pepper. Barbecue corn, turning as needed, for 10 mins or until charred all over and tender. Slice kernels from corn cobs.
Divide iceberg slabs among 4 plates and sprinkle with salt and pepper. Spoon dressing over lettuce. Top with chicken, corn kernels, cucumber, tomatoes, green beans and more dressing.