Article on mature cooked ham (7)
I believe the answer is:
amateur
'ham' is the definition.
(I've seen this before)
'article on mature cooked' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'on' is an insertion indicator.
'cooked' indicates an anagram.
'mature' is an anagram of 'amteur'.
'a' put into 'amteur' is 'AMATEUR'.
(Other definitions for amateur that I've seen before include "he won't get paid" , "Unpaid (sport)" , "Non-pro" , "Unpaid (sports)" , "incompetent" .)