Begin second quiche (5)
I believe the answer is:
start
'begin' is the definition.
(I know that start is a more specific form of begin)
'second quiche' is the wordplay.
'second' becomes 's' (common abbreviation).
'quiche' becomes 'tart'.
's'+'tart'='START'
(Other definitions for start that I've seen before include "Begin to recoil?" , "begin an argument?" , "launch" , "open" , "lead" .)