Heat a 3-qt. sauce pan over medium-high heat and add the olive oil.
Add the leek, celery, carrot, bay leaf and sauté for 1 minute.
Add garlic, stir well and sauté for 1 minute longer.
Add the chicken breasts, chicken stock and thyme sprig. Bring contents up to a boil. Lower heat and simmer for about 20 minutes, skimming off foam and fat.
Remove the chicken breasts and set aside to cool.
Remove the meat from the bones and dice or shred into small pieces. Add to the soup. Check the seasoning and adjust if necessary. Add the chopped parsley. Remove the bay leaf and thyme sprig.
Serve with Matzoh Balls.