In 3 1/2 to 4-quart slow cooker, layer chicken, mushrooms and roasted pepper strips. Drizzle with sherry. Evenly pour Alfredo sauce on top.
Cover; cook on low setting for 5 to 6 hours.
About 25 minutes before serving, rinse broccoli with warm water to thaw; drain well. Add broccoli to chicken mixture. Increase heat setting to high; cover and cook an additional 20 minutes. Meanwhile, cook fettuccine to desired doneness as directed on package. Drain.
Just before serving, stir cooked fettuccine into chicken mixture. Sprinkle with Parmesan cheese.