Next, prepare the steak. Place a large skillet pan over medium-high heat. Let it heat for 2-3 minutes until very hot. While heating, generously salt and pepper one side of the steak, and sprinkle with the Montreal steak seasoning.
Once pan is hot, add a drizzle of oil to the bottom of the pan, just enough to lightly cover the bottom of the pan. Carefully place the steak (seasoned side down) into the hot pan, being careful to not burn yourself. It will sizzle.
While the first side is searing, season the top side with more salt, pepper, and Montreal steak seasoning. Sear for 4-6 minutes per side, depending on how thick your steak is, and how done you'd like it. (I did 5 minutes per side for medium.)
Once seared on each side, remove from heat with tongs and let steak rest on a cutting board for 5 - 10 minutes.
Once rested, slice steak into thin strips. Sprinkle on a little more salt once sliced, to make sure each slice gets some salt. Set aside until ready to build sandwich.