Next, add 2 tbsp cooking oil, the onions and mushrooms. Sauté those until nice and tender. Then, set your burner to 275 degrees.
On the opposite side of the onions, keeping that side on sear mode, sear the steaks, for about 3 minutes. Add seasoning to them! Salt and pepper works great.
Now flip them and let them sear for one more minute. After the minute is up, chop the steaks with the spatula, and mix the onions and mushrooms with it incorporating everything.
At this time turn your heat to low and separate the mixture into 3 separate smaller portions, about the length of the buns.
Now add 3 slices of Swiss cheese per portion and turn your heat off on the griddle, ( just on the section the steak is on) the steam from the meat will melt it.
On another section where the heat is still on, toast the buns. Add butter to the griddle and lay down the buns. Toast then until golden brown.
Now add the buns to the steak portions and scoop everything into the buns. Let cool for 3 min before serving.
Notes
You can use any cut of steak for this cook, you can always ask your local butcher to thinly slice some steak.