Preheat the oven to 350 degrees F.
In a large skillet pan (or large sauté pan), over medium-high heat, add the olive oil, sliced green bell pepper, sliced onion, kosher salt, and black pepper. Cook until the vegetables are softened and slightly caramelized, stirring occasionally- about 10 minutes.
1 tablespoon olive oil, 1 green bell pepper, 1 sweet onion, ½ teaspoon kosher salt, ¼ teaspoon black pepper
Push the vegetables to the side of the skillet and add the thinly sliced shaved steak. Season the steak with the Worcestershire sauce, garlic powder, onion powder, kosher salt, and black pepper. Cook the steak until browned and cooked through - about 5-6 minutes.
1 tray (14 ounces) shaved steak, 1 tablespoon Worcestershire sauce, 1 teaspoon garlic powder, ½ teaspoon onion powder, ½ teaspoon kosher salt, ¼ teaspoon black pepper
Toss the steak with the vegetables to combine all the ingredients together in the skillet pan.
Cut the slider buns in half horizontally, making sure to keep the bottom as one whole piece and the top of the sliders in one whole piece. Place the bottom piece into a 9x13 baking pan (or something similar that will fit the sliders).
12 King's Hawaiian Slider Rolls
Spoon the onion and steak mixture over top the slider buns inside the baking pan. Evenly layer the provolone cheese over top the steak, and then sprinkle the mozzarella cheese on top. Cover with the top piece of slider buns.
6 slices provolone cheese, ¾ cup shredded mozzarella cheese
In a small mixing bowl, stir together the melted butter, garlic powder, and dried parsley. Spread the melted butter mixture over top the slider buns using a pastry brush.
4 tablespoons butter, 1 teaspoon garlic powder, 1 teaspoon dried parsley
Cover the entire baking dish with aluminum foil and then bake for 10 minutes. If the cheese has not fully melted, remove the foil, and continue baking for an additional 3-5 minutes.
Serve the Philly cheese steak sliders immediately. Enjoy!