Preheat the oven to 350°F. Lightly grease a 9-inch deep-dish pie plate or similar baking dish.

Cook the spaghetti in salted boiling water until al dente according to package directions. Drain well and set aside.

Heat olive oil in a large skillet over medium heat. Add the ground beef and diced onion. Cook until the beef is browned and the onion is softened.

Add the minced garlic and cook for 30 seconds, stirring often.

Drain excess grease from the skillet if needed. Stir in the marinara sauce, Italian seasoning, salt, and black pepper. Simmer for 5 minutes, then remove from heat.

In a large bowl, whisk together the eggs and 1/4 cup Parmesan cheese.

Add the cooked spaghetti to the egg mixture and toss until evenly coated.

Press the spaghetti mixture into the prepared pie plate, spreading it evenly across the bottom and slightly up the sides.

Spread the ricotta cheese over the spaghetti layer.

Spoon the meat sauce evenly over the ricotta layer.

Sprinkle the top with 1 cup mozzarella cheese and the remaining 1/4 cup Parmesan cheese.

Bake uncovered for 25 to 30 minutes, or until the cheese is melted, bubbly, and lightly golden.

Remove from the oven and let the spaghetti pie rest for 10 minutes before slicing.

Garnish with fresh parsley if desired, then serve warm.