Coin placed in a vegetable (6)
I believe the answer is:
'coin' is the definition.
(I have seen 'Spanish coin' mean 'peseta' so perhaps 'coin' could also mean 'peseta')
'placed in a vegetable' is the wordplay.
'placed' becomes 'set' (synonyms).
'in' is an insertion indicator.
'a vegetable' becomes 'pea' (pea is a type of vegetable).
'set' put within 'pea' is 'PESETA'.
(Other definitions for peseta that I've seen before include "Old Spanish currency" , "Domestic social" , "Former Spanish monetary unit" , "Spanish bread once" , "Old unit of money in Spain" .)