In a large pot, bring salted water to a rolling boil. Add the spaghetti and cook according to the package instructions until al dente, approximately 8-10 minutes. Once cooked, drain and set aside in a large mixing bowl.
In a separate large mixing bowl, whisk together the cream of chicken soup, sour cream, shredded cheddar cheese, canned diced tomatoes with green chilies, chopped onion, minced garlic, Italian seasoning, black pepper, and salt. Mix until all ingredients are fully incorporated and smooth.
In the bowl with the drained spaghetti, add the shredded chicken. Pour the prepared sauce mixture over the spaghetti and chicken, using a spatula to gently fold everything together until well combined.
Preheat your oven to 350°F (175°C). Generously grease a 9x13-inch baking dish with cooking spray or butter. Pour the spaghetti mixture into the prepared dish and spread it evenly with the spatula.
Evenly sprinkle the grated Parmesan cheese over the top of the spaghetti mixture to create a cheesy crust that will crisp as it bakes.
Carefully place the baking dish in the preheated oven. Bake for 25-30 minutes, or until the top is a beautiful golden brown and bubbly, indicating it is thoroughly heated.
Once baked, remove the dish from the oven and allow it to cool for a few minutes. Just before serving, garnish with chopped fresh parsley for a burst of color and flavor.
Notes
Pair with a crisp green salad and garlic bread for a complete meal.