Preheat your oven to 400°F (200°C). Lightly oil a 9x13 inch baking dish.

In a large mixing bowl, combine the ground beef, bread crumbs, milk, salt, Worcestershire sauce, pepper, minced onion, parsley, and eggs. Mix gently to combine and form into 1-inch meatballs.

Arrange the meatballs on a baking sheet and bake for 18-20 minutes until cooked through and lightly browned.

Bring a large pot of salted water to boil. Add spaghetti and cook 1-2 minutes less than package instructions for al dente. Drain and toss with olive oil.

In the pot with the drained spaghetti, add an egg, chopped parsley, mozzarella, and parmesan. Stir until well combined.

Spread the spaghetti mixture evenly in the baking dish, place meatballs on top, and pour sauce over everything.

Cover with aluminum foil and bake at 350°F (175°C) for 35 minutes.

Remove the foil, sprinkle remaining mozzarella and parmesan cheese over the casserole and bake for another 10 minutes until golden and melted.

Let the casserole rest for 5 minutes before serving.