Cook the Spaghetti
Preheat your oven to 375°F (190°C). Cook the spaghetti in a large pot of salted boiling water until al dente, according to package instructions. Drain and set aside.
Prepare the Cheese Sauce
In a large skillet or saucepan, combine the softened cream cheese, sour cream, and chicken broth over medium heat. Whisk until smooth and creamy. Stir in the ranch seasoning, garlic powder, onion powder, and 1 cup of shredded cheddar cheese.
Assemble the Casserole
In a large mixing bowl, combine the cooked spaghetti, shredded chicken, crumbled bacon (reserving some for topping), and the cheese sauce. Mix until well coated.
Transfer to Baking Dish
Lightly grease a 9x13-inch baking dish. Spread the spaghetti mixture evenly in the dish. Sprinkle the remaining cheddar cheese, mozzarella cheese, and reserved bacon on top.
Bake
Place the casserole in the preheated oven and bake uncovered for 20–25 minutes, or until bubbly and golden on top.
Cool and Serve
Allow the casserole to rest for 5 minutes before serving. Garnish with fresh parsley if desired.