Preheat your oven to 350°F (177°C).

Fill a large pot with water and bring it to a rolling boil. Add salt and cook the spaghetti until al dente, about 8–10 minutes. Drain and set aside.

In the same pot, combine cubed cream cheese and stir gently with residual heat until melted and smooth, about 3–5 minutes.

Add the drained spaghetti, pasta sauce, and diced tomatoes to the melted cream cheese. Stir thoroughly for 2–3 minutes until well-coated.

Mix half of the shredded cheese into the spaghetti mixture, then transfer to a greased casserole dish, spreading evenly.

Sprinkle the remaining shredded cheese over the top of the mixture in the casserole dish.

Bake for 30–35 minutes until the cheese is bubbling and golden brown.

Let the dish cool for about 15 minutes before serving. Garnish with basil or red pepper flakes if desired.