Heat the olive oil in a large Dutch oven or deep skillet over medium-high heat. Add the ground beef and diced onion, then cook for 5 to 7 minutes while breaking up the meat, until the beef is browned and the onion is softened.

Drain excess fat if necessary, especially if the beef is not very lean. Add the minced garlic, Italian seasoning, kosher salt, and black pepper, and cook for 30 to 60 seconds until fragrant.

Stir in the crushed tomatoes, diced tomatoes, and low-sodium broth. Add the dry spaghetti and press it down into the liquid as much as possible.

Bring the mixture to a boil, then reduce the heat to medium-low and cover the pot. Simmer for 12 to 15 minutes, stirring every few minutes so the spaghetti does not stick together or settle on the bottom.

Continue cooking until the spaghetti is tender and the sauce has thickened. If the pasta remains firm, add a small amount of water or broth and cook a little longer.

Taste the sauce and adjust the seasoning as needed. Serve each portion with grated Parmesan and chopped fresh parsley if desired.