Can anybody tell me how to bind a click/tap event to a cluster?

I can bind it to the marker that my theme uses, but I can't tell how to go from there to get the cluster.

What I would like to do with this is to click on a cluster and get the map to zoom in on the points that belong to that cluster. I can do that, I just can't figure out how to attach the event listener to the cluster.

Cheers
David