Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and lightly grease a 9x13 inch baking dish.
Bring a large pot of salted water to a boil and cook spaghetti until al dente according to package directions, then drain.
In a large mixing bowl, combine the shredded chicken, condensed soup, chicken broth, diced onion, diced bell pepper, garlic powder, black pepper, salt, and 1 cup of the shredded cheddar cheese.
Add the cooked spaghetti to the bowl and toss until the noodles are thoroughly coated in the sauce mixture.
Transfer the mixture to the prepared baking dish and spread into an even layer.
Top the casserole with the remaining 1 cup of shredded cheddar cheese.
Bake for 30 minutes or until the cheese is melted and the edges are bubbling.