The option to disable the auto mesh function is not yet available on Dashboard with the current releases.
I would echo Philip and recommend to give us a call on the support number, as can definitely work our magic for you 😉
meraki support can definitely do this. we asked them to enable it for one of our customer sites which gives you a tickbox under network-wide settings
For anybody looking for this, as I was, and couldn't find it in the Meraki Documentation (a lot about Mesh, but nothing about turning this option off). With current firmware there is a tickbox under Network-wide General config under the section "Device Configuration". You can turn the automatic mesh off.
BUT …… (very unfortunately that this option is not documented properly) …. IT WILL DISCONNECT ALL clients. I didn't notice any AP restart, but all clients lost connection for a short period of time. Very odd this happened, because there is no reason for that since both my two AP's are connected to the LAN switch.