1Bring a large pot of salted water to a boil and cook the spaghetti until al dente. Reserve 1/2 cup pasta water and drain.
2While the pasta cooks, heat the frozen meatballs in the marinara sauce in a dutch oven over medium-low heat for about 15 minutes, stirring gently, until piping hot.
3Loosen the sauce with a splash of pasta water if it looks thick.
4Toss the spaghetti with a little sauce, plate it, and top with meatballs, extra sauce, chopped parsley and parmesan.