Preserve cooked meal doctor's tucking into (6)
I believe the answer is:
embalm
'preserve' is the definition.
(as in embalming a body)
'cooked meal doctor's tucking into' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'doctor' becomes 'MB' (Bachelor of Medicine).
'tucking into' means one lot of letters goes inside another.
'meal' with letters rearranged gives 'ealm'.
'ealm' enclosing 'mb' is 'EMBALM'.
(Other definitions for embalm that I've seen before include "Preserve corpse from decay" , "Treat corpse with preservatives" , "Prepare corpse for preservation (6)" , "Treat corpse so as to retard decay" , "Preserve from decay in death with chemicals" .)