Add the butternut squash, brussel sprouts, and parsnips to a large bowl. Drizzle over the olive oil and sprinkle over the rosemary, garlic powder, salt, and pepper. Toss to combine.
2 cups cubed butternut squash, 2 cups halved Brussels sprouts, 2 cups cubed parsnips, 3 tablespoons olive oil, 1 teaspoon minced fresh rosemary, 1 teaspoon garlic powder, 1 teaspoon kosher salt, ½ teaspoon ground black pepper