Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, brown the ground beef until fully cooked. Drain excess fat.
Add chopped onion and garlic to the skillet and sauté until softened.
Stir in the marinara sauce, diced tomatoes, oregano, basil, salt, and pepper. Allow the mixture to simmer for about 10 minutes, letting the flavors meld together.
While the sauce simmers, cook the spaghetti according to package instructions until al dente. Drain and set aside.
Combine the cooked spaghetti with the sauce in the skillet, mixing well to coat all the pasta.
Transfer the spaghetti mixture to a large baking dish. Sprinkle the mozzarella and Parmesan cheeses evenly over the top.
Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly with a golden crust.
Remove from the oven and let it sit for a few minutes before serving. Garnish with fresh parsley if desired.
Variations & Tips
For a healthier twist, use ground turkey or chicken instead of ground beef. To add some veggies to the dish, sauté bell peppers, mushrooms, or spinach along with the onions and garlic. If you have picky eaters, consider making a half-and-half version with plain spaghetti on one side and the full sauce mix on the other. For extra flavor, you can mix in a bit of ricotta cheese with the pasta before baking.