Code:
On *:Input:*: {
  if (.list == $1) {
    tokenize 124 $1-
    var %sdir = $gettok($1,$+(2,-,$numtok($1,32)),32)
    if (%sdir) {
      var %x = 1
      while (%x <= $findfile(%sdir,$iif($2,$2,*.*),0)) {
        echo -a $+([,$findfile(%sdir,$iif($2,$2,*.*),%x),])
        inc %x
      }
      halt
    }
  }
}


.list <directory>|<extension>

Example:

.list C:\mIRC|*.ico

Lists all *.ico files.

If you don't specify an extension:

Example:
.list C:\mIRC

Lists all files in mIRC.

-Andy