Begin small quiche (5)
I believe the answer is:
start
'begin' is the definition.
(I know that begin can be written as start)
'small quiche' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'quiche' becomes 'tart'.
's'+'tart'='START'
(Other definitions for start that I've seen before include "Onset" , "Begin to recoil?" , "Move quickly < when surprised" , "lead" , "Opening - jump" .)