Preheat the oven to 350°F (175°C) and apply non-stick spray or butter to a 9x13 inch ceramic or glass baking dish.

Fill a large stockpot with water, add a generous pinch of salt, and bring to a rolling boil. Cook the spaghetti until al dente according to package specifications. Drain thoroughly and set aside.

In a large skillet over medium-high heat, heat the olive oil. Add the diced onion and sauté for 4-5 minutes until translucent.

Add the ground beef to the skillet. Brown the meat, using a spatula to break it into small crumbles, until no pink remains. Drain any excess accumulated fat.

Incorporate the minced garlic, Italian seasoning, salt, and black pepper into the beef. Cook for 60 seconds until the garlic is aromatic.

Pour the marinara sauce into the beef mixture. Reduce heat to low and simmer for 10 minutes to allow the flavors to integrate.

In a separate large mixing bowl, combine the warm cooked spaghetti with the alfredo sauce. Toss until every strand is evenly coated in the cream sauce.

Transfer the alfredo-coated spaghetti to the prepared baking dish, spreading it into an even base layer.

Distribute the meat marinara sauce evenly over the top of the spaghetti layer, extending it to the edges of the dish.

Sprinkle the shredded mozzarella and grated parmesan cheese uniformly over the meat sauce layer.

Place the dish in the center of the oven and bake for 25 to 30 minutes, or until the cheese is melted, bubbly, and beginning to turn golden brown.

Remove from the oven and allow the dish to rest for 10 minutes to set the layers. Garnish with fresh parsley before slicing and serving.