Turned on a chubby little chap (7)
I believe the answer is:
rounded
'turned' is the definition.
'on a chubby little chap' is the wordplay.
'on' is an insertion indicator (as in clothing 'on' a person).
'a chubby little' becomes 'unde' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chap' becomes 'Rod'.
'unde' going into 'rod' is 'ROUNDED'.
Can you help me to learn more?
(Other definitions for rounded that I've seen before include "Complete and balanced; made curved" , "(Of the lips) pursed" , "full" , "Well-developed; balanced" , "Plump" .)