Place turkey carcass in large pot and cover with cold water. Larger turkeys can be cut or broken into smaller pieces. It's not necessary to completely cover the carcass. Add a bay leaf or 2.
Bring water to boil, then reduce temperature to a simmer, covering partly with lid to allow steam to escape as the broth simmers. Press down carcass periodically to help turkey break up and remain under most of the water. Simmer for about 3 hours.
Remove turkey from broth and strain liquid. Allow turkey to cool enough to handle, then remove as much meat as possible.
Meanwhile, chop onion, celery and carrots. Add to strained broth. Taste and season with salt and pepper. Add chicken bouillon if more flavour is desired. Simmer for 30 minutes.
Break vermicelli into pieces and add to soup. Simmer for 10 minutes.
Add frozen peas and fresh parsley, heating only until peas are warm.