Preheat oven to 350°F (175°C). Grease a 9x13 inch baking dish.
Cook spaghetti in salted water until al dente, about 2 minutes less than package directions.
Melt butte In a large skillet, melt butter over medium heat . Sauté onions, bell peppers, and mushrooms until softened.
Add minced garlic and cook for 1 minute, just until fragrant.
In a large bowl, combine soups, chicken broth, sour cream, and seasonings.
Add cooked vegetables, shredded chicken, and 1 cup of cheese to the mixture.
Fold in cooked spaghetti until well combined.
Transfer the mixture to a prepared baking dish and sprinkle with the remaining cheese. .
Bake in a preheated oven at 350°F (175°C) for 30-35 minutes, or until bubbly and golden brown.
Let rest for 10 minutes before serving. Garnish with fresh parsley.