I'm trying out Andy's solution here and have a couple of thoughts:
It seems like if you have a windowed action then you are doubling up on the opening of a main incident window to edit the details.
If a call is 'In Review' you would then open it up to complete the mandatory data and save and close. The next action that you have would be the 'Complete Mandatory Fields' action which would pop up the window again. I was using a windowless action but wanted to use a precondition to check for mandatory fields rather than having to click an extra action.
I understand why I can't use a precondition now but wondered if there was a way around having to click another button that would say something like 'Incident Details Complete' It Just seems like extra clicks that can be forgotten