A siesta in garden apartment (3)
I believe the answer is:
nap
'a siesta' is the definition.
(I've seen this before)
'in garden apartment' is the wordplay.
'in' indicates the answer is hidden within the clue.
'NAP' is hidden within 'garden apartment'.
(Other definitions for nap that I've seen before include "A short day-sleep" , "Sleep lightly" , "Sleep briefly" , "Little sleep" , "Racing tip that professes to be a certainty" .)