Diet average, I am breaking fast (10)
I believe the answer is:
parliament
'diet' is the definition.
(I've seen this before)
'average i am breaking fast' is the wordplay.
'average' becomes 'par' (average score in golf).
'breaking' is an insertion indicator.
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'i'+'am'='iam'
'iam' placed into 'lent' is 'liament'.
'par'+'liament'='PARLIAMENT'
(Other definitions for parliament that I've seen before include "UK legislature" , "Legislative body" , "Houses" , "Diet" , "Legislative assembly" .)