Mirror on left Charlie smashed (7)
I believe the answer is:
reflect
'mirror' is the definition.
(I've seen this before)
'on left charlie smashed' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'smashed' is an anagram indicator.
'left'+'c'='leftc'
'leftc' is an anagram of 'flect'.
're'+'flect'='REFLECT'
(Other definitions for reflect that I've seen before include "Think - what mirrors do" , "Cogitate" , "Think or mirror" , "Act as a mirror" , "'Ponder, chew over (7)'" .)