Turkish commander popular -- encore! (5)
I believe the answer is:
again
'encore' is the definition.
(I've seen this in another clue)
'turkish commander popular' is the wordplay.
'turkish commander' becomes 'aga' (term for an Ottoman military commander).
'popular' becomes 'in' ('in' can mean trendy).
'aga'+'in'='AGAIN'
(Other definitions for again that I've seen before include "Next time" , "'Another time, once more (5)'" , "Here we go ___" , "Moreover - a second time" , "One more time, encore" .)