Rinse and pat dry chicken. Place in a 5-quart or larger crockery slow cooker. Place the peeled and quarterd onion, peeled and quartered carrot, and parsley around chicken pieces. Sprinkle with thyme, marjoram, and pepper.
Add chicken broth, cover, and cook on low for 7 to 8 hours or on high for 2 1/2 to 3 hours.
When done cooking, remove the chicken and discard the onion, carrot, and parsley. Skim off and discard all surface fat from the broth.
Cool chicken from broth for about 10 minutes, until cool enough to handle and remove and discard the chicken skin and bones. Shred chicken.
Add shredded chicken back to the slow cooker and bring to a simmer. Lightly saute the diced onion, diced carrots, diced celery, mushroom, in a little broth or water until softened and place in the crock along with the spinach. Simmer for 10 minutes.
Meanwhile, cook noodles according to package directions.
Just before serving, add cooked noodles to soup and season with salt and pepper (to taste).