Greek tucked into a tuna I cooked, covered in breadcrumbs (2,6)
I believe the answer is:
au gratin
'covered in breadcrumbs' is the definition.
'greek tucked into a tuna i cooked' is the wordplay.
'greek' becomes 'gr' ().
'tucked into' is an insertion indicator.
'cooked' indicates an anagram.
'a'+'tuna'+'i'='atunai'
'atunai' with letters rearranged gives 'auatin'.
'gr' inserted within 'auatin' is 'AU GRATIN'.
(Other definitions for au gratin that I've seen before include "Crumby" , "Served with browned cheese and breadcrumbs" , "Like some dishes" , "Scattered" , "Cooked with grated cheese and/or breadcrumbs" .)