Mince the garlic in a food processor. Add the tarragon and chives, and process until minced. Add the rest of the ingredients and process until smooth. Taste, and adjust seasoning as required.
Preheat the barbecue.
Chop the vegetables into desired sizes. Push on to the skewers. Brush with olive oil so all sides are coated. Season with salt and pepper. Grill for approximately 15 minutes, rotating every 5 minutes. When cooked and slightly charred, remove kebabs from the grill. Drizzle with the dressing and serve immediately.