Preheat the Oven
Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish or coat it with non-stick spray.
Cook the Spaghetti
Bring a large pot of salted water to a boil. Cook the spaghetti according to the package instructions until al dente. Drain the spaghetti and set it aside.
Prepare the Cream Cheese Sauce
In a large mixing bowl, combine the softened cream cheese and sour cream. Mix well until smooth. Add in the marinara sauce, garlic powder, Italian seasoning, and a pinch of salt and pepper. Stir until everything is fully combined and creamy.
Combine the Spaghetti and Sauce
Add the cooked spaghetti to the cream cheese sauce mixture. Gently toss the pasta to ensure each strand is coated with the creamy sauce.
Assemble the Casserole
Transfer the coated spaghetti into the prepared baking dish. Spread the pasta evenly in the dish. Sprinkle the shredded mozzarella cheese and grated Parmesan cheese evenly over the top of the pasta.
Bake
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes. After 20 minutes, remove the foil and continue baking for an additional 10 minutes, or until the cheese on top is melted and bubbly.
Serve
Remove from the oven and let it cool for a few minutes before serving. Garnish with fresh parsley or extra Parmesan cheese, if desired.