Add all of the casserole ingredients into the slow cooker, apart from the flour.
Cook on high for 4 hours or low for 5-6 hours. I always start with 1 hour on high. If you need to leave it longer you can easily cook for 8-10 hours, or overnight.
One hour before serving stir through the flour (diluted in a little water)
If you're having dumplings then add them for the final hour. I always make them smaller than when I'm cooking them in the slow cooker so that one hour is enough time.
Add lots more vegetables if you want to bulk this out. They will release a little juice, which will help create more stock too.