A nut to chew when interrupting (6)
I believe the answer is:
cashew
'a nut' is the definition.
(cashew is a kind of nut)
'chew when interrupting' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'interrupting' means one lot of letters goes inside another.
'chew' enclosing 'as' is 'CASHEW'.
'to' is the link.
(Other definitions for cashew that I've seen before include "Kidney shaped nut" , "Kind of nut" , "nut-tree" , "Common type of nut" , "Acajou" .)