Cassoulet is a goodie and quite a lot of leftovers can be incorporated; I've used left-over cooked chicken, sausages, Spam, ham, belly pork would also work well.
There's a zillion ways to make it and of course tinned or dry pulses can be used. I tend to use tinned 'cos we generally have 'em around and no pre-cooking required,
It's a French peasant dish and pretty-much anything could be added. A quick Google brings-up any number of recipes.
Basic starter version
Large casserole:
Fry-off any meats as required* Meat-free version would be fine too.
Brown onions +/- Celery.
Primary pulse should be Flageloet beans as they provide the texture, but Lentils and any other kind of pulse can also be added alongside (just drain and rinse). I also like to add frozen broad-beans.
Tinned or fresh Chopped toms depending on availability
Wine or stock to ensure solids covered
Loads of Garlic
Bay leafs
Thyme sprigs or Parsley
Salt and loads of pepper.
Bring to the boil and either: Bung in the slow cooker and bugger-off or in the oven at 150 for about 2 hrs.
Final consistency should be slightly fatty with the Flegeleot beans just turning slightly mushy though other pulses may be firmer.
Breadcrumbs and/or grated cheese may also be added prior to serving.
*Sausages any kind to suit really, English, German, (or you can use Chorizo type sausages) cook and slice.
Ham, belly pork, spam. bacon bits.
Cooked chicken thigh (dark) meat, duck, goose.