Have you ever taken on a job that you were unqualified for?
In your example, show how you are not afraid of taking risks to achieve goals at work. Demonstrate your focus on the job at hand and how it inspired others.
For instance, I took on management responsibilities in my previous position to take the place of my manager who had left. I did not have any management experience but I knew that the team was not going to be able to be effective without a leader in place. I may have made a few mistakes, but ultimately was successful in taking on that additional responsibility. The upper level management were impressed by my growth and efforts so they ended up promoting me into that position.