Interrupting prayer, I'm to make a face (7)
I believe the answer is:
grimace
'make a face' is the definition.
(synonyms)
'interrupting prayer i'm' is the wordplay.
'interrupting' is an insertion indicator.
'prayer' becomes 'grace' (grace is a kind of prayer).
'grace' going around 'im' is 'GRIMACE'.
'to' is the link.
(Other definitions for grimace that I've seen before include "Glower" , "Ugly facial expression" , "Distortion of the face" , "Pull a face" , "(Make) a wry face" .)