Make the sauce. In the basin of a slow cooker, mix together the cream of chicken soup, diced tomatoes, green pepper, cream cheese, 2 cups of cheddar cheese, salt, garlic powder, onion powder, and cayenne pepper until well combined.
Add the chicken. Add the chicken to the slow cooker and spoon some sauce over it to cover.
Cook. Seal the slow cooker and cook on low for 6 hours.
Make the spaghetti. 20 minutes before the cooking time is up, fill a large pot with water and bring it to a boil. Add the salt. Cook the spaghetti in the salted water according to the directions on the package. Drain the spaghetti, reserving 1 cup of the pasta water.
Shred the chicken. Remove the chicken from the slow cooker and shred it with two forks. Stir it back into the sauce.
Put it all together. Stir the spaghetti into the sauce until every noodle is thoroughly coated. If the sauce is having a hard time adhering to the pasta, stir in a bit of the reserved pasta water.
Serve. Serve warm garnished with fresh parsley.
Notes
If you don't have any diced tomatoes on hand, feel free to grab a can of Rotel and use the tomatoes with green chilies in place of the diced tomatoes. The Rotel tomatoes are perfect, but the green chilies will add a little spice to the dish.