Cook spaghetti on top of the stove in boiling water. Cook bacon on rack in microwave on high 6-7 minutes, covered. Crumble and set aside.
Add butter to dish with mushrooms and onions. Cook on High 4-5 minutes, stirring once. Stir in flour and pepper. Cook at high 30 seconds. Add broth and 1/2 & 1/2, mix well and cook on High 9-10 minutes, stirring every 2 minutes. Add sherry (if desired). Stir in cooked spaghetti, chicken, bacon and parmesan. Mix well. cover and cook at High 13-15 minutes, stirring once. Garnish with parsley.
Serves 6-8. Great for using leftover turkey after Christmas or Thanksgiving.