Cooking ingredient, as it happens, stuffing two ducks I left (5,3)
I believe the answer is:
olive oil
'cooking ingredient' is the definition.
(I've seen this before)
'as it happens stuffing two ducks i left' is the wordplay.
'as it happens' becomes 'live' (as in live television).
'stuffing' indicates putting letters inside.
'two ducks' becomes 'oo'.
'left' becomes 'l' (common abbreviation).
'live' inserted within 'oo' is 'oliveo'.
'oliveo'+'i'+'l'='OLIVE-OIL'
(Other definitions for olive oil that I've seen before include "dressing maybe" , "Pressed liquid used in cooking, medicine, soaps etc" , "Liquid used in cookery or salad dressings" , "Viscous liquid from green or black fruit" , "Ingredient of salad dressing" .)