User facing planar texture (not user facing poly)

I am wondering how I would achieve a particular look.

Imagine the texture is static, a flat plane behind a 3d mesh. The mesh is a viewport that allows you to see the flat plane, the mesh is static and doesn’t move as you walk around but the plane moves behind it to constantly facing the player. This would be the appearance but obviously you wouldn’t want it achieved quite like this as you want to have shading too.