Most convenient siesta, half abandoned in orient (7)
I believe the answer is:
easiest
'most convenient' is the definition.
(I've seen this before)
'siesta half abandoned in orient' is the wordplay.
'half' suggests halving the letters.
'abandoned' is an anagram indicator (the original order is abandoned).
'in' indicates putting letters inside.
'orient' becomes 'east' (synonyms).
'siesta' cut in half is 'sie'.
'sie' anagrammed gives 'ies'.
'ies' placed inside 'east' is 'EASIEST'.
(Other definitions for easiest that I've seen before include "Least hard" , "most amenable" , "most like pie" , "Most convenient" , "Most effortless" .)