Fruit crisp or pie, storebought, would be tasty and go well with this menu. The combination of onion, celery, and carrot is known in French cuisine as a mirepoix . It forms the flavor in many dishes from chicken soup to sauces. You may use it as the base for creating other quick soups. If you can find flat-leaf parsley, by all means use it.
Curly parsley is long on looks and short on flavor.
Be sure to rinse it well before you use it.