Cook pancetta or bacon in oil in a 12-inch nonstick skillet over medium heat, stirring occasionally, until just beginning to brown, about 5 minutes. Add onion and salt and cook, stirring, until onion is softened, about 4 minutes. Add noodles and cook, stirring, 1 minute. Add peas and broth to skillet and bring mixture to a boil. Cook, stirring, until noodles are just tender, about 3 minutes.
Remove skillet from heat and stir in butter, Parmesan, and pepper. (If mixture is a bit soupy, let it stand for 1 to 2 minutes to allow noodles to continue to absorb liquid.) Serve with additional Parmesan, if desired.
