Framing bathroom mirrors - a great tutorial with step-by-step instructions & pictures. glue the molding right on to the mirror. I did this in my bathroom, not hard and a very inexpensive way to update a plain mirror.
How To Build A Wood Frame Around A Bathroom Mirror
How to frame bathroom mirror that has plastic clips - thinnest washer poss. clip 1 @ a time. same screw & swap out clips with washer. Moulding will fit flat against wall. liquid nails to secure moulding.