Simple way to achieve financial security (4,6)
I believe the answer is:
easy street
'simple way to achieve financial security' is the definition.
(I've seen this before)
'simple way' is the wordplay.
'simple' becomes 'easy' ('easy' is associated in meaning with 'simple').
'way' becomes 'street' (street is a kind of way**).
'easy'+'street'='EASY STREET'
(Other definitions for easy street that I've seen before include "affluence" , "Simple way to achieve financial security" , "State of financial security" , "Comfortable state of life" , "one appreciated by deliveryman?" .)