Bring a large pot of salted water to a boil. Cook the pappardelle according to package directions. Drain and reserve.
Heat a large pan over medium heat. Add the olive oil and sauté the onions until softened and starting to brown (about 3 minutes). Add the peas and meatloaf. Stir in the ketchup and ¼ cup water. Bring to a simmer. Toss in the pasta.
Divide between 4 bowls. Sprinkle with the Parmigiano.