Chew some pork that’s medium on the inside (5)
I believe the answer is:
chomp
'chew' is the definition.
(chomping is a kind of chewing)
'pork that's medium on the inside' is the wordplay.
'pork' becomes 'chop' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'that's medium' becomes 'm' (as in UK clothing sizes).
'on the inside' means one lot of letters goes inside another.
'chop' going around 'm' is 'CHOMP'.
'some' acts as a link.
Can you help me to learn more?
(Other definitions for chomp that I've seen before include "Chew" , "For crunch" , "Munch noisily (colloq.)" .)