Left Charlie and Oscar under one colonnade (7)
I believe the answer is:
portico
'under one colonnade' is the definition.
'portico' can be an answer for 'colonnade' (I've seen this in another clue). I'm not sure about the 'under one' bit.
'left charlie and oscar' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'charlie' becomes 'ic' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'port'+'ic'+'o'='PORTICO'
Can you help me to learn more?
(Other definitions for portico that I've seen before include "Entrance with a roof supported by columns" , "A number of columns" , "Zeno's teaching colonnade" , "Colonnade in front of a building" , "Covered entrance with columns" .)