Combine first 4 ingredients; drizzle with 2 teaspoons olive oil. Toss. Arrange mixture on a baking sheet; bake at 400° for 40 minutes or until cauliflower is tender and golden, stirring twice. Cook pasta according to package directions, omitting salt and fat. Drain in a colander over a bowl, reserving 1/2 cup cooking liquid.
Heat a large skillet over medium heat. Add pancetta to pan, and cook for 5 minutes or until crisp, stirring frequently. Remove pancetta; set aside. Add remaining 2 1/2 teaspoons oil to drippings in pan. Add 1/2 cup reserved cooking liquid to drippings in pan; bring to a boil over high heat. Boil 30 seconds or until emulsified, stirring constantly with a whisk. Add rind, juice, thyme, and garlic to pan. Add pasta; toss. Remove from heat. Add cauliflower and pancetta; toss. Top with cheese. Serve immediately.