Preheat the oven to 350 degrees F. Set out a large baking sheet and line it with parchment paper.
Use a serrated knife to cut the rolls in half to make tops and bottoms. You can leave each package of rolls attached to make the cutting faster. Then move both “bottom sheets” of rolls to the prepared pan. (Save the tops for later.)
Cut the provolone slices into quarters and place a quarter-slice of cheese on top of each roll's bottom half.
Place a large 12-14 inch skillet over medium-high heat. Add 3 tablespoons butter to the skillet. Once melted, add in the onions. Sauté for 3-5 minutes, moving around the pan.
Once the onions are partially cooked, add in the chopped bell pepper. Sauté and stir another 3-5 minutes. Then move the sautéed vegetable to a holding plate.
Add the remaining 3 tablespoons butter to the empty skillet. Place the shaved steak in the skillet, along with the Italian seasoning, garlic powder, 1 teaspoon salt, and ¼ teaspoon black pepper. Stir and sear the steak, for 3-5 minutes until fully cooked. Then turn off the heat and add in the onions and peppers. Taste, then salt and pepper as needed.
Scoop the steak mixture evenly over the roll bottoms and cheese. Place 24 dollops of Cheez Whiz over the steak mixture, one dollop per roll. Then place the two “top sheets” of rolls over the Cheez Whiz.
Bake in the oven until the tops are slightly crusty and the cheese is melted. Serve warm.
You can find packages of pre-shaved steak in the meat department of most major grocery stores.The shaved steak will stick together as it cooks, so make sure to move it around the pan and break it up a bit, if needed.Make-Ahead Tip: Make the beef and pepper mixture ahead of time, cool and store in an airtight container in the fridge for a day or two. Then assemble and bake the sandwiches when ready to enjoy!The beef sliders are definitely best when enjoyed fresh and warm from the oven. Leftovers can be stored in an airtight container in the fridge for up to 2 days; note that the bread will become softer and soggy the longer it sits.