Slice the steak across the grain as thinly as possible. Place the slices into a medium-sized bowl. Sprinkle with the Cajun seasoning and toss to coat.
Arrange an oven rack 6-inches from the top of the oven. Preheat the oven to 400℉.
Heat a large skillet over medium-high heat, and add 1 teaspoon oil. Swirl to coat the pan. Add half of the seasoned meat and spread across the pan. Cook for 1 minute, and then use a large spatula or tongs to flip them over. Cook for 1 minute. If you still have some red spots on the meat, just turn it over and cook until done. You want the meat to be crispy and brown on the outside and juicy in the middle. Remove the cooked meat to a bowl, add the rest of the meat to the pan and repeat.
Add the butter to the skillet. Add the cooked meat back in and stir to coat with the butter, scraping up browned bits in the bottom of the pan.
Open the sandwich rolls and spread them across a large baking tray. Divide the steak onto the bottom half of each roll. Sprinkle cheese over the steak. Place the open sandwiches in the oven for 3 to 4 minutes, until the bread is toasted and the cheese melts. Keep an eye on the rolls; they will go from toasted to burned in moments. Beware!
Notes
We skipped peppers, onions and mushrooms (which are usually spotted on a traditional cheesesteak sandwich), but you can certainly add those in if you prefer!