Boil the chicken in some water. Once the chicken is cooked remove the chicken and keep the water or in this case chicken broth. In a separate pan sautés the onions, celery, and bell pepper in the butter until tender. Boil the spaghetti in the chicken broth. Do not drain. Once the spaghetti is done remove it from the stove and all all other ingredients. Pour into a casserole dish and sprinkle generously with cajun seasoning. Bake at 325 degrees for 30 minutes. Then serve! I like to top mine with even more cajun seasoning.