Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente.
Reserve a small cup of the pasta cooking water, then drain the pasta in a colander.
Return the drained pasta to the pot over low heat, add the cauliflower sauce and 1/4 cup grated Parmesan, and toss to combine; add a splash of reserved pasta water if needed to loosen the sauce.
Season with salt and pepper to taste and stir until evenly coated and heated through.
Serve immediately, sprinkled with additional Parmesan and chopped parsley.