Pre-heat the oven to 375ºF (190 ºC)
In a cooking bowl, mix the butter and oil with the milk, the stock and the stuffing mix.
Arrange the chicken cubes in the bottom of a 13x9 slightly greased
casserole dish. Display the mushroom slices and layer the Swiss cheese.
Pour the juices over and poke a bit with a fork to be sure everything gets to the bottom.
Cover with the mashed potatoes, tap on with a spatula and top with sprinkled parmesan cheese.
Let it bake until it starts to bubble in the middle, around 35-40 minutes.