Preheat your oven to 350°F (175°C).
In a large pot, cook the spaghetti according to package instructions until al dente. Drain and set aside.
In a mixing bowl, combine the softened cream cheese, sour cream, Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper. Mix well until creamy and smooth.
Add the cooked spaghetti to the cream cheese mixture and stir until the pasta is evenly coated.
Pour half of the marinara sauce into the bottom of a 9x13 inch baking dish.
Layer the spaghetti and cream cheese mixture on top of the marinara sauce, spreading it evenly.
Top with the remaining marinara sauce and sprinkle the shredded mozzarella cheese on top.
Cover the baking dish with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 5 minutes, or until the cheese is bubbly and slightly golden.
Remove from the oven and let it cool for a few minutes before serving. Garnish with fresh parsley if desired.