Bring a large pot of water to a boil. Add the chicken pieces to the boiling water and boil for a few minutes, then return the heat to medium-low and simmer, 30 to 45 minutes.
Preheat the oven to 350 degrees F
Remove the chicken and set aside 2 cups of the chicken cooking broth from the pot. When the chicken is cool, break up and also set aside
Dice peppers and onion, set aside. Saute mushrooms until they’ve given up their and have browned slightly
Add some olive oil to the mushrooms and saute onion and peppers with a fat pinch of salt.
Add 1 cup of the set aside chicken broth to the vegetables to deglaze. Add the cream of mushroom soup and green chilis to the vegetables and simmer on low adding an additional cup if needed.
Break up and cook the spaghetti in the pot of broth until al dente
When the spaghetti is cooked, drain and return the pasta to the pot
Add the chicken, mushroom soup, vegetables, cayenne. 1 1/2 cups cheese to the pot of pasta
Mix Well
Place the mixture in a casserole pan and top with the remaining 1 cup cheese and bake immediately until bubbly, about 45 minutes. (If the cheese on top starts to get too cooked, cover with foil).