Meanwhile, in a large skillet, cook bacon over medium heat until crisp. Using a slotted spoon, remove to paper towels to drain. Brown mushrooms in drippings; remove to paper towels. Drain drippings from pan.
Add the cream, butter, parsley, garlic, pepper sauce and salt if desired to the skillet; cook and stir over medium heat until butter is melted. Drain mostaccioli; add to cream mixture. Stir in the bacon, mushrooms and cheese; heat through. Remove from the heat. Sprinkle with green onions.