Pea to augment soup (9)
I believe the answer is:
'pea' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'to augment soup' is the wordplay.
'soup' indicates anagramming the letters.
'toaugment' is an anagram of 'MANGETOUT'.
Can you help me to learn more?
(Other definitions for mangetout that I've seen before include "vegetables" , "Vegetable" , "Edible pea pods" , "Type of pea" , "Sugar peas" .)