1. Preheat oven to 425°. Toss sprouts with 1 tablespoon oil; arrange cut side down on a baking sheet. Sprinkle with salt, pepper, and pancetta. Roast 18–20 minutes or until sprouts are tender.
2. Meanwhile, cook pasta according to package directions. Drain, reserving 1/4 cup cooking water. Return pasta to pot.
3. Add garlic to sprouts; toss well. Add sprouts, Parmesan, thyme, and a few tablespoons reserved pasta water to pasta; stir in remaining 2 teaspoons oil. Spoon into 4 bowls; sprinkle with hazelnuts.