Hardy companion, eschewing starter, eats fresh tuna plainly cooked (2,7)
I believe the answer is:
au naturel
'plainly cooked' is the definition.
(I've seen this before)
'hardy companion eschewing starter eats fresh tuna' is the wordplay.
'hardy companion' becomes 'laurel' (as in the comedy duo Laurel and Hardy).
'eschewing' indicates named letters should be taken away.
'starter' becomes 'l' (as in a learner driver with L-plates on their car).
'eats' means one lot of letters goes inside another.
'fresh' indicates anagramming the letters (a fresh re-ordering of the letters).
'laurel' with 'l' taken out is 'aurel'.
'tuna' is an anagram of 'unat'.
'aurel' going around 'unat' is 'AU NATUREL'.
(Other definitions for au naturel that I've seen before include "In the nude - in France" , "Cooked plainly - naked" , "Cooked plainly or raw" , "Plain" , "Very simply" .)