Place the potatoes in a small pot and cover with water. Season with salt, cover and boil until fork-tender, about 6 minutes. Drain and cool. Meanwhile, pulse the chives, tarragon, vinegar, yogurt, 1/2 teaspoon salt, and pepper to taste in a food processor. Slowly drizzle in theolive oil and pulse to make a thick dressing. Toss the romaine, potatoes, chicken, cucumber, radishes and bell pepper with the dressing in a large bowl. Season with salt and pepper.