Open the map compiler and click on the button for advanced options (">>>"), there you'll see a slider "Tesselate flat".

IMO you should not use vertex lighting, though, but use simple point light shaders (without any normalmapping and the like). Then you don't need tesselation anyway.

EDIT: Because vertex lighting always looks bad, no matter how fine your tesselation is, and it's basically only a relict from old A5/ A6 times.