Flatter veal pieces filling mean sandwich (7)
I believe the answer is:
palaver
'flatter' is the definition.
(thesaurus)
'veal pieces filling mean sandwich' is the wordplay.
'pieces' is an anagram indicator (the same pieces in a new order).
'filling' is an insertion indicator.
'mean sandwich' becomes 'par' (I can't explain this - if you can you should give a lot more credence to this answer).
'veal' is an anagram of 'lave'.
'lave' going within 'par' is 'PALAVER'.
Can you help me to learn more?
(Other definitions for palaver that I've seen before include "(Talk of a) conference" , "Commotion" , "Yak" , "Fuss and bother" , "Confused talk and activity" .)