When designers have to communicate decisions to stakeholders, one possibility is to use a requirements document. Another strategy could be using something different in order to avoid the risk of "taking a couple of days to get everyone on the same page": the task analysis grid is an interesting alternative to the standard requirements documents.
The aim is to see the entire scope of the project and the whole features of the first and future releases on the same page in a unique schematic description.
How is it structured?
Each column starts out with a scenario, describes a task and is followed by all the sub-tasks necessary to complete the task. The sub tasks are colour-coded and prioritized. Influencers and pain-points are highlighted for each task in order to complete the whole description.