Mess is eating place serving meat loaf (8)
I believe the answer is:
scrapple
'loaf' is the definition.
(I know that scrapple is a type of loaf)
'mess is eating place' is the wordplay.
'mess' becomes 'scrape' (I can't justify this - if you can you should believe this answer much more).
'is eating' is an insertion indicator.
'place' becomes 'pl' (abbreviation used in postal addresses).
'scrape' placed around 'pl' is 'SCRAPPLE'.
'serving meat' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for scrapple that I've seen is " Meatloaf".)