Maybe Holly Hunter wants filling in sandwich (5)
I believe the answer is:
shrub
'maybe holly hunter' is the definition.
I can't judge whether this definition defines the answer.
'filling in sandwich' is the wordplay.
'filling' becomes 'hr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'sandwich' becomes 'sub' (sub is a kind of sandwich).
'hr' inserted within 'sub' is 'SHRUB'.
'wants' acts as a link.
Can you help me to learn more?
(Other definitions for shrub that I've seen before include "Woody plant, bush" , "box, say" , "Perhaps Heather" , "Elder" , "Drink of rum, fruit juice and spices" .)