Needing no introduction, wench one lad’s seen with — a Mexican dish! (9)
I believe the answer is:
enchilada
'mexican dish' is the definition.
(enchilada is a type of Mexican dish)
'needing no introduction wench one lad's seen with a' is the wordplay.
'needing no introduction' means to remove the first letter.
'one' becomes 'i' (Roman numeral).
'seen with' says to put letters next to each other.
'wench' with its initial letter taken off is 'ench'.
'ench'+'i'+'lad'+'a'='ENCHILADA'
(Other definitions for enchilada that I've seen before include "hot dish" , "spicy food" , "Rolled stuffed tortilla with chilli sauce" , "Tortilla and sauce, meat" , "Hot food" .)