Very large portion of chicken or moussaka (8)
I believe the answer is:
enormous
'very large' is the definition.
(I've seen this before)
'portion of chicken or moussaka' is the wordplay.
'portion of' indicates the answer is hidden within the clue.
'ENORMOUS' is hidden in the letters of 'chicken or moussaka'.
(Other definitions for enormous that I've seen before include "Huge, really big" , "Gross" , "Huge, tremendous" , "Tremendous, gigantic" , "Extraordinarily large" .)