Preheat oven to 350°F (175°C). Lightly grease a 2-quart baking dish.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water until tender yet firm to the bite, about 12 minutes. Drain.
Mix cream of chicken soup, drained tomatoes with green chile peppers, cooked chicken, and cooked spaghetti together in a large bowl. Pour the mixture into the prepared baking dish.
Top with shredded Cheddar cheese.
Bake in the preheated oven until the cheese is melted and bubbling, about 30 minutes.