Let users add reviewers to a pull-request using groups.
The plugin adds a button to the Pull Request Creation form & Edit Pull-Request Dialog: "Add Reviewers From Group". Clicking on this button will open a dialog with a list of groups that has permission to the repository & project.
The user can check a box next to each group (or select all). Members from each group will then be added into the reviewers field.
This is an open-source plugin, see: https://github.com/Cyanoth/Bitbucket-PullRequest-ReviewerGroups for more information.