Seat sis mended breaks in Spain (7)
I believe the answer is:
'breaks in spain' is the definition.
(a siesta is a short sleep taken in Spain)
'seat sis mended' is the wordplay.
'mended' indicates anagramming the letters.
'seatsis' with letters rearranged gives 'SIESTAS'.
(Other definitions for siestas that I've seen before include "Assets I hide during naps" , "Afternoon naps" .)