Place chicken into a sauce pan and add water to cover. Simmer over low heat, 60-90 minutes. Low and slow makes the chicken tender.
Remove chicken and turn the heat up to high and bring the water, which is now chicken broth, to a boil. Add 1 T salt and spaghetti and cook until just done. Do not overcook.
Drain pasta and chop chicken.
Saute onion and peppers in a skillet with a drizzle of Olive oil. Season with salt and pepper. Add Rotel, tomatoes, soup and cheese. Cook and stir until cheese has melted.
Place 1/2 of spaghetti into a large mixing bowl. Add the chicken. Pour sauce over all and stir gently. Add the rest of the pasta gradually, stirring until it has the sauce to pasta ratio you like. I kept mine pretty creamy so it wouldn't dry out during baking. At this point the casserole can be refrigerated for up to 2 days. Bake at 325 for 45-60 minutes. Serves 4-6