In a large skillet or cooking pot, saute bell pepper and onion in olive oil.
Add 1 can of chicken broth and chicken. Simmer until tender. Cut chicken into bite-size pieces as it's cooking. Use 3 cups of chicken. (you can use packaged chicken tenderloins or cooked chicken from the deli. Whatever is convenient. It's all good.)
Add all soups and Ro-tel tomatoes. Stir well. Simmer for about 15 minutes until chicken is done.
Cook the spaghetti in boiling water or chicken broth until just slightly cooked "al dente" - you don't want to over-cook it because it will be cooking more in the oven. Drain, rinse, and set aside until you are ready to mix with chicken/sauce ingredients in baking dish for the oven.
In a large baking dish or oven-proof pot, place the cooked and cut up chicken, cooked spaghetti, salt and pepper, cheese, and soup mixture.
Depending on how creamy you like this dish, you may want to add extra chicken broth before you bake. (I always do).
Stir very well to mix all ingredients evenly.Stir once again after about 15 minutes in the oven - after the cheese has had time to melt. Bake at 375 degrees for 30 minutes.
You can add canned or fresh mushrooms if you like (optional).
You can add one can of black olives, sprinkled over the top of the casserole. (optional)