Do you eat them cooked? And do all of them cause you diarrhea? And if I may add... if you are going for the iron, better aim for meat, no?
-Are you flaring at the moment? if no,
-As it been like that most of your life? (some people lack the enzyme to digest the vegetable, that could be some sort of intolerance).
-Do you tolerate juice? Sometime juice extraction might do the job but... that might probably not help the craving...
Except boiled vegetables, to avoiding diarrhea, I doubt there is much ways to avoid it from raw veggies... unfortunaly. Potatoes have some iron, but they aren't really satisfying when you want to eat veggies... I find green bean easy to digest... cooked (sigh).
Sorry, If I'm not much help I don't really know If there is a way, maybe there is and ill be happy to read it too if someone knows the secret