Add onion, carrots, celery, and garlic; cook for 5 minutes or until softened.
Bring to a gentle boil, and add pre-cooked chicken chunks.
Stir in the noodles. Reduce heat and simmer, covered, for 10 minutes or until noodles are tender, stirring occasionally.
Stir in parsley, salt, and pepper to taste.
Ladle into soup bowls, garnish with onion, and serve with thick slices of bread.