From NSF Proposal & Award Policies & Procedures Guide (PAPPG), January 2018:
Postdoctoral Researcher Mentoring Plan. Each proposal that requests funding to support postdoctoral researchers must upload under “Mentoring Plan” in the supplementary documentation section of FastLane, a description of the mentoring activities that will be provided for such individuals. In no more than one page, the mentoring plan must describe the mentoring that will be provided to all postdoctoral researchers supported by the project.
View the Postdoctoral Researcher Mentoring Plan sample template.