Simple painting perhaps separating bridge (7)
I believe the answer is:
spartan
'simple' is the definition.
(I've seen this before)
'painting perhaps separating bridge' is the wordplay.
'painting perhaps' becomes 'art' (painting is a kind of art).
'separating' indicates putting letters inside.
'bridge' becomes 'span' (synonyms).
'art' put into 'span' is 'SPARTAN'.
(Other definitions for spartan that I've seen before include "Indifferent to comfort" , "Ascetic - ancient Greek" , "Plain" , "Austere - disciplined" , "Of conditions, harsh and lacking comforts" .)