Preheat the oven to 425 degrees F.
Place the carrots, bell pepper, sweet potato, onions, and garlic on a rimmed baking sheet. Drizzle with olive oil and salt, and toss to coat. Roast until the vegetables are tender and golden brown, about 24-26 minutes.
Meanwhile, bring a large pot of salted water to a boil over high heat. Cook the pasta according to package directions. (If not using broth: Remove 1¼ cup of the pasta cooking water and set aside to reserve.) Drain the pasta, and return it to the pot.
Transfer the roasted vegetables to a blender with the broth (or pasta cooking water) and marinara sauce. Blend until smooth and creamy, adding as much of the pasta cooking water (or broth, if using) as needed to make a smooth sauce.
Add as much of the sauce to the cooked pasta as you like and toss to coat.
Serve immediately with additional salt, and Parmesan, fresh basil, and/or black pepper as you like.
