Fish dish, head removed, filled with new parsley, perhaps (7)
I believe the answer is:
garnish
'parsley perhaps' is the definition.
'fish dish head removed filled with new' is the wordplay.
'fish' becomes 'gar' (gar is a kind of fish).
'head removed' means to remove the first letter.
'filled with' is an insertion indicator.
'new' becomes 'n'.
'dish' with its first letter taken off is 'ish'.
'gar'+'ish'='garish'
'garish' enclosing 'n' is 'GARNISH'.
(Other definitions for garnish that I've seen before include "Decorate food for table" , "Add a trimming to a dish" , "Decorate, embellish" , "It's added to a dish for flavour or decoration" , "Decorate food for sharing" .)