Is there a distinction between 肉夹馍 (ròujiāmó) and 馍夹肉 (mójiāròu)?
The second is just right-to-left writing.  See  Horizontal_and_vertical_writing_in_East_Asian_scripts .
Historically, Chinese was written in vertical columns, with columns progressing from right to left.  In the 20th century a shift was made so that most writing is in rows, from left to right.  


  Today, the left-to-right direction is dominant in [Chinese, Japanese,
  and Korean] ... However, right-to-left horizontal writing is still
  seen in these scripts, in such places as signs [and]  stands selling
  food at festivals.


Think of the right to left horizontal writing as showing just a top character in each of a series of columns from right to left.