Discuss inserting pinch of spice as sauce ingredient (7)
I believe the answer is:
parsley
'sauce ingredient' is the definition.
(ingredient in parsley sauce)
I don't understand how the remainder of the clue works.
(Other definitions for parsley that I've seen before include "Herbal garnish" , "Culinary herb" , "Green plant" , "Aromatic herb with flat or crinkly leaves" , "plant used in cooking" .)