Bring a large pot of salted water to a boil. Add spaghetti and cook according to package instructions until al dente. Drain and set aside.

Heat olive oil in a large skillet over medium heat. Add chopped onion and cook for about 3 to 4 minutes until softened. Add minced garlic and cook for about 30 seconds until fragrant.

Add ground beef to the skillet. Cook for 6 to 8 minutes, breaking it apart as it cooks, until browned. Drain excess fat if needed.

Stir in tomato sauce, diced tomatoes, Italian seasoning, Worcestershire sauce, red pepper flakes, salt, and black pepper. Let the sauce simmer for about 10 minutes so the flavors blend together.

In a large mixing bowl, combine the cooked spaghetti and meat sauce. Add 1 cup mozzarella, ½ cup cheddar, and ¼ cup parmesan cheese. Mix until the pasta is evenly coated.

Preheat oven to 375°F (190°C). Lightly grease a 9×13 baking dish. Transfer the spaghetti mixture into the dish and spread evenly. Top with the remaining mozzarella, cheddar, and parmesan cheese.

Bake uncovered for 25 to 30 minutes until the cheese is melted, bubbly, and slightly golden.For a crispier top, broil for the last 2 minutes.

Let the baked spaghetti rest for 5 minutes before serving. Garnish with fresh parsley desired. Serve warm and enjoy.