While the pasta is cooking, stir in the cheeses in small amounts, stirring and melting as you go. Season with salt and pepper to taste. Once the cheese is melted, add reserved bacon and green onions. Return the sauce to almost boiling and keep warm until the pasta is ready. Once the pasta is cooked, remove 2 cups of the pasta water in a glass measuring cup then drain and add the pasta to the sauce. Toss with the last 1 tablespoon truffle oil. Serve immediately, garnished with fresh chopped parsley.