What's cooking? Copper is, in midfield (7)
I believe the answer is:
cuisine
'what's cooking?' is the definition.
(eg French cuisine is French cooking)
'copper is in midfield' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'in midfield' becomes 'ine' (I can't justify this - if you can you should believe this answer much more).
'cu'+'is'+'ine'='CUISINE'
Can you help me to learn more?
(Other definitions for cuisine that I've seen before include "Style of cookery" , "French cooking?" , "(Regional) style of cooking" , "Culinary art" , "Local cooking style" .)