Cook the spaghetti according to the package instructions. Drain and set aside.
In a large skillet, cook the ground beef over medium heat until browned. Add the chopped onion and minced garlic, and cook until the onion is translucent.
Stir in the marinara sauce and Italian seasoning. Season with salt and pepper to taste. Simmer for 10 minutes.
In a large baking dish, layer half of the cooked spaghetti, half of the meat sauce, and half of the shredded cheeses. Repeat the layers with the remaining spaghetti, meat sauce, and cheeses.
Bake in the preheated oven for 30 minutes, or until the cheese is melted and bubbly.
Let the casserole cool for a few minutes before serving. Enjoy!
Notes:
This dish can be made ahead and refrigerated until ready to bake.