Breakfast food firm breaks an embargo (5)
I believe the answer is:
bacon
'breakfast food' is the definition.
(I've seen this before)
'firm breaks an embargo' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'breaks' means one lot of letters goes inside another (inserted letters break into the word).
'an embargo' becomes 'ban' (a ban on trade).
'co' inserted within 'ban' is 'BACON'.
(Other definitions for bacon that I've seen before include "famous artist" , "modern artist" , "rasher" , "Eg, rashers" , "Writer of essays" .)