No Physical Output Device / VNC Display: a mess of overlapping content

[codeclinic]

I recently setup a MagicMirror on a Pi 3B+ with a physical monitor attached and all went well. Today I was hoping to get things setup with the various modules that I require. To do this I was hoping to VNC into the box for visual checks whilst using SSH for implementing the modules etc.

However, without a physical monitor attached via HDMI and using VNC all the modules output is a mess of overlapping content. Is there a way to force the screen resolution so that appears as expected via VNC ?

Thanks.