Preheat oven to 350°F (180°C).

Cook spaghetti in boiling, salted water for 8-10 minutes, until al dente.

Drain spaghetti and set aside.

Sauté ground beef in a large skillet over medium-high heat, breaking it up with a spoon, until browned, about 5-7 minutes.

Add diced onions to the skillet and cook until translucent, about 3-4 minutes.

Stir in canned crushed tomatoes, tomato paste, and dried basil, bringing the mixture to a simmer.

Reduce heat to low and let sauce simmer for 10-15 minutes, stirring occasionally, until thickened.

Combine cooked spaghetti, sauce, and shredded mozzarella cheese in a large bowl, tossing until spaghetti is well coated.

Transfer spaghetti mixture to a 9x13-inch baking dish and top with additional shredded mozzarella cheese.

Bake in the preheated oven for 25-30 minutes, until cheese is melted and bubbly, and the top is golden brown.

Remove from oven and let cool before serving.