Press leftover stuffing (or mix) into a 9" pie or quiche pan to form crust. Bake for 10-15 minutes. Stuffing should have a slight crust. After removing stuffing crust from oven, reduce oven temperature to 375 degrees F.
In a medium bowl, mix turkey, milk, eggs, cheese and onions together. Pour mixture into stuffing crust. Bake quiche for 30 minutes or until just firm.