Sales talk about origin of lamb dish (7)
I believe the answer is:
platter
'dish' is the definition.
(platter is a kind of dish)
'sales talk about origin of lamb' is the wordplay.
'sales talk' becomes 'patter' (sales patter).
'about' is an insertion indicator.
'origin of' says to take the initial letters.
The initial letter of 'lamb' is 'l'.
'patter' enclosing 'l' is 'PLATTER'.
(Other definitions for platter that I've seen before include "Charger" , "Salver" , "main course" , "old record?" , "Shallow serving dish" .)