Line two rimmed baking sheets with parchment paper.
Spread parsnips onto one pan, and carrots and yellow onion onto the other. Spray vegetables lightly with cooking spray. (This adds flavor with very little oil.)
Roast for 15 minutes. Flip veggies over and roast for another 10-15 minutes or until tender. (Note: The onions may need to come out earlier than the other vegetables.)
While the vegetables are roasting, dry-sauté mushrooms for 8 minutes over medium heat using a nonstick pan or a regular pan coated in cooking spray.
Add garlic to pan and sauté for another 2 minutes, until garlic is fragrant but not burned. Add a small splash of water if needed to prevent sticking.
Add roasted veggies, mushrooms, garlic, fresh herbs, salt, and pepper to a large food processor. Pulse until the veggies have a confetti texture. (Don't over-process!)
Add additional salt and pepper if desired, and serve warm.
Notes
Adding sweetened dried cranberries gives a pop of color and extra holiday flavor!