Boil spaghetti in well seasoned chicken broth and drain. Saute onion ... Pour into buttered casserole; bake at 375 degrees for 20 minutes or until bubbly.
Combine soups, broth, and tomatoes ... Place layer of chicken, half of the sauce, ... in a 13"x9" casserole. Repeat for second layer ... for another 15 minutes.
Cook chicken ahead of time and reserve ... bottom of 9"x13" casserole dish. On top of tortillas ... If you like Rotel or green chilies, add to soup mixture. Rotel are spicier.