Heat the olive oil over medium-high heat in a shallow pot or a large, deep skillet. When the oil is hot but not smoking, add the turkey and salt. Stir well to combine, then arrange it in one layer. Cook for 3 minutes.
Stir well. Continue cooking for 3-4 minutes until the turkey is no longer pink and any liquid has cooked away. Stir often while breaking up large pieces with a wooden spoon or spatula.
Lower the heat to medium and add the onions. Cook for 2-3 minutes, stirring occasionally.
Add the garlic, tomato paste, Italian seasoning, and black pepper. Cook for 1-2 minutes, stirring frequently.
Add the diced tomatoes and pasta sauce. Stir well while gently scraping any bits off the bottom of the pot.
Let the sauce come to a simmer (this will take 2-3 minutes). Then, lower the heat to medium-low and cover. Cook the sauce for 30 minutes.
Stir occasionally and keep the sauce at a simmer. Raise or lower the heat as needed.
In the meantime, bring a large pot of water to a boil. Cook the spaghetti to package directions for al dente. Before draining, reserve 1-2 cups of the pasta cooking water. Drain the spaghetti well.
Taste the sauce and add salt if needed. As a reference, we did not add extra to ours.
Serve the pasta with the meat sauce. Garnish with chopped parsley and serve with parmesan cheese and crushed red pepper, if desired.