Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and lightly grease a 9x13 inch baking dish.
Cook the spaghetti noodles in a large pot of boiling salted water until al dente according to package instructions, then drain.
In a large mixing bowl, whisk together the cream of mushroom soup, cream of chicken soup, chicken broth, diced onion, green bell pepper, garlic powder, salt, and black pepper.
Fold the shredded chicken and undrained diced tomatoes with green chilies into the soup mixture.
Add the cooked spaghetti and 1 cup of the shredded cheddar cheese to the bowl and toss until the noodles are thoroughly coated.
Transfer the mixture to the prepared baking dish and spread it into an even layer.
Sprinkle the remaining 1 cup of shredded cheddar cheese over the top.
Bake for 30 minutes or until the sauce is bubbling and the cheese on top is fully melted and lightly golden.
Remove from the oven and let stand for 5 minutes before serving.