Your face already has a uv, you just have to 're lay' them out in a neat order, in your four pane view click>panels/panel/uv texture editor, go to object more and select the face object, then click edit polygons/texture/ and click either planar/cylindrical/spherical or automatic mapping for your uv layout, try each one for the 'best' uv layout, then adjust your UVs by right clicking and selecting UVs in the viewport and moving them until they are no longer over lapping and look like a flat clean mesh.

Hope this helps.