Bring a pat of water to boil, add salt to taste, then cook the pasta according to packet instructions.
Meanwhile, whisk together the oil, lemon juice, salt and mustard to make the dressing.
Drain the cooked pasta and tip it into a large bowl, pour over the dressing and toss well to coat.
When cool stir in the mortadella pieces, chopped parsley, if using, and Parmesan. Check the seasoning adding salt and pepper as required.