Craves a three-wheeler that's fast (6,6)
I believe the answer is:
hunger strike
'fast' is the definition.
(hunger strike is a kind of fast)
'craves a three-wheeler' is the wordplay.
'craves' becomes 'hungers' ('hunger' can be a synonym of 'crave').
'a three-wheeler' becomes 'trike' (I've seen this before).
'hungers'+'trike'='HUNGER-STRIKE'
'that's' is the link.
(Other definitions for hunger strike that I've seen before include "fast" , "Non-violent protest" , "Starvation protest" .)