I cooked it with cod, I must be daft! (7)
I believe the answer is:
idiotic
'daft' is the definition.
(thesaurus)
'i cooked it with cod i' is the wordplay.
'cooked' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'cod'+'i'='codi'
'it' put after 'codi' is 'codiit'.
'codiit' with letters rearranged gives 'diotic'.
'i'+'diotic'='IDIOTIC'
'must be' acts as a link.
(Other definitions for idiotic that I've seen before include "Mindless" , "without any point" , "Inviting ridicule" , "without intelligence" , "Absurd, crackbrained" .)