Heat a medium skillet over medium heat; add bacon and onion. Cook, stirring often, until onion starts to brown, about 10 minutes.
Meanwhile, heat a large saucepan of water to a boil; add gnocchi, cook according to package directions. Drain, reserving about 1/2 of the cooking water.
Add some of the cooking water to the skillet; cook, stirring, to make a sauce. Add parsley, tomatoes, salt and pepper. Heat, about 1 minute. Add gnocchi; toss to coat. Serve with Parmesian cheese, if desired.