Add the chicken thighs and boil for a few minutes, then turn the heat to medium-low and simmer for around 40 minutes.
Remove the chicken and reserve 2 cups of the resulting broth.
When the chicken is cool, remove the skin and pick off all the meat. Discard the bones and skin.
Next, preheat the oven to 300 F.
Cook the spaghetti in the water used for cooking the chicken and boil it for around 8 minutes until al dente.
Drain the spaghetti and combine it in a large bowl with the chicken, 1 ½ cups of shredded cheddar, diced red and green peppers, cayenne, two cans of soup, and diced onions, and sprinkle in salt and pepper to taste.
Stir in 1 cup of reserved chicken broth, adding an additional cup if needed.
Transfer the mixture to a large casserole pan and top it with the remaining 1 cup of cheese.
Bake immediately for 45 minutes or until it begins to bubble.