Employers might ask this question to understand what you consider to be your most valuable accomplishments. To answer, think about a recent example that is ideally related to the job in some way.
Like, "Last year, my team won an award for coming up a most innovative project. My role was to organize the team to breakthrough ways we could speed up the team production process. We found three ways and implemented the one that worked best for us. The process took less time and came up with double output".