There's a worm, cooked, right inside the vegetable! (6)
I believe the answer is:
marrow
'the vegetable' is the definition.
(marrow is a kind of vegetable)
'there's a worm cooked right inside' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'cooked' indicates anagramming the letters (letters cooked into a new form).
'right' becomes 'r' (common abbreviation).
'inside' means one lot of letters goes inside another.
'a' next to 'worm' is 'aworm'.
'aworm' is an anagram of 'marow'.
'marow' going around 'r' is 'MARROW'.
(Other definitions for marrow that I've seen before include "Connective tissue in bones" , "essence" , "essential part" , "Stuff found inside bones" , "Large vegetable gourd or stuff in bones" .)