In a large skillet, heat 2 tbsp. EVOO over medium heat. Add the onions and cook, stirring occasionally, until softened and golden, 15 to 20 minutes.
Meanwhile, in a small saucepan, warm the Cheese Whiz over low heat. Preheat a griddle or cast-iron skillet over medium- high heat. Lightly coat the griddle or pan with EVOO. Throw the steak down on the griddle and cook for about 45 seconds. Flip, season with salt and pepper and cook, turning occasionally, until cooked through. Stir the sauteed onions into the beef, then transfer to a cutting board and coarsely chop together.
Smear the melted Cheese Whiz on both open faces of the rolls. Pile in the beef and onions. Cut the cheesesteaks in half and eat right away.