Show it's duck meat (6)
'show it's' is the definition.
I can't judge whether this defines the answer.
'duck meat' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'meat' becomes 'liver' (liver is a kind of meat).
Can you help me to learn more?
(Other definitions for oliver that I've seen before include "One taking pride in food", "Orphan recruited by criminal gang", "A Cromwell, a Twist", "Musical from Dickens novel", "Cromwell, for example".)