I downloaded the latest Raspian Stretch Lite 2018-03-13 for my PiZero 1.2 (no camera connector or WiFi), used a console connection to enable ssh, then in raspi-config, I enabled boot into GUI and VNC.
Connecting with VNC I got a mini 200x300 pixel window only.
I've had that before, and knew that all you have to do is change the resolution in raspi-config, which I did - but this time with no effect!
I tried disabling and re-enabling one or two of the original steps with no effect.
I slept on it (usually works a treat) and this morning I searched for all files with vnc in their filename hoping to find the relevant config file, but drew a blank. There's no /home/pi/.vnc which I might have expected, and the /root/.vnc contains nothing relating to screen resolution. If I could just find my mini/standard HDMI adapter I'd have tried a real screen.
Maybe I should have done things in a different order, but in any case there would seem to be a missing screen resolution line in a config file somewhere which should have been inserted automatically.
Regards - Philip