Make the Cauliflower Alfredo: Fill a large sauce pan halfway with water and bring to a boil. Add cauliflower pieces and boil for 30 minutes or until tender. Reserve 1/2 cup cooking water, then drain. Dissolve bouillon in reserved cooking water. In a food processor, combine cooked cauliflower, bouillon mixture, Parmesan, and 1/4 teaspoon salt. Process to form a creamy sauce. Transfer to a large skillet to keep warm and season to taste with salt, black pepper, and nutmeg (if using).
Season chicken with salt and pepper. In large skillet brown chicken and mushrooms 4 minutes in hot oil, turning chicken halfway through.
Meanwhile, shred 2 teaspoons lemon peel; set aside. Slice lemon. Add broccoli and lemon slices to skillet. Cover; cook 8 minutes or until chicken is done (170 degrees F on an instant-read thermometer).
Evenly distribute Alfredo on four plates. Top with chicken and vegetables.