Pre-heat oven to 400°F.
Place garlic powder, mustard, 2 tsp. ground pepper, 2 tsp. salt in a bowl. Combine into a paste for marinating the roast.
Toss brussel sprouts, rutabagas, and veggie mix with 2 Tbsp. oil, 4 Tbsp. of butter, 4 sprigs of thyme and season with salt and pepper. Place the vegetables into a roasting pan.
Rub the roast with the marinade mixture and place in the middle of the roasting pan on top of some of the vegetables. Place in oven and cook the roast until probe thermometer reaches 50°C, about 30-45 minutes.
Remove the roast from the oven and let rest on a separate rack in a warm place for about 10 minutes.
While the roast is resting, toss the roasted vegetables with parsley and adjust seasoning with salt and pepper.