No chicken sandwiches in Washington? What an idea! (9)
I believe the answer is:
brainwave
'an idea' is the definition.
(I've seen this before)
'no chicken sandwiches in washington?' is the wordplay.
'no chicken' becomes 'brave' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sandwiches' indicates putting letters inside (inserted letters are sandwiched in).
'washington?' becomes 'wa' (abbreviation for the US state).
'in'+'wa'='inwa'
'brave' placed around 'inwa' is 'BRAINWAVE'.
'what' is the link.
Can you help me to learn more?
(Other definitions for brainwave that I've seen before include "Sudden bright idea" , "Good idea" , "Great idea" .)