Preheat oven to 400°F. Line a sheet tray with foil and lightly drizzle with olive oil or spray with cooking spray.
In a large bowl, toss and coat the vegetables with the olive oil, salt, and pepper. In one layer, spread the vegetables out on the sheet tray. Add the thyme and rosemary in different areas of the sheet tray on top of the vegetables.
Roast for 15 minutes and then gently stir the vegetables. Roast for an additional 10 to 15 minutes, or until the vegetables are tender. Discard the rosemary and thyme.
In a medium-sized bowl whisk together the yogurt, milk, garlic, onion, salt, mustard, pepper, chives, parsley, and dill. Serve vegetables with ranch sauce.