Seasoning lamb, as illustration shows (5)
I believe the answer is:
basil
'seasoning' is the definition.
(basil is a kind of seasoning)
'lamb as illustration shows' is the wordplay.
'shows' says the answer is hidden in the clue.
'BASIL' can be found hidden inside 'lamb as illustration'.
(Other definitions for basil that I've seen before include "Man" , "Fragrant herb" , "Aromatic plant used as a herb" , "Name of male" , "Aromatic herb with purplish-green leaves" .)