You can ask support to enable a switch in the dashboard for your network to turn off meshing. I recently asked for this, as I was seeing a WEP encrypted hidden SSiD from every Meraki AP being broadcast on both 2.4ghz and 5ghz (these are used for the meshing functionality), and wanted to cut down on unnecessary radio/SSi'd on our network (as we do not or have plans to use meshing)
Unfortunately, even after turning off the meshing option in dashboard, you will still see these hidden ssid's broadcasting on your network.
Meraki tell me that they cannot turn these networks off, they are permanently on by design !!