Prepare the Dressing: In a medium-sized mixing bowl, combine the olive oil, Italian seasoning, garlic powder, onion powder, and salt. Whisk the ingredients thoroughly until they are well blended. Set this mixture aside; it will be used as the flavorful dressing for the sliders.
Preheat the Oven: Before assembling the sliders, preheat your oven to 350°F (175°C). To ensure easy cleanup, line a 9×13 baking dish with parchment paper or lightly grease it with cooking spray.
Slice the Slider Buns: Using a serrated knife, carefully slice the slider buns horizontally into two halves, ensuring the top and bottom sections remain intact. Place the bottom halves of the buns evenly into the prepared baking dish.
Layer the Ingredients: Begin by arranging the provolone cheese slices evenly across the bottom halves of the buns. Chop the turkey, salami, and pepperoni into smaller pieces to make them easier to distribute. Layer these chopped meats on top of the cheese, creating a hearty and flavorful base. Sprinkle the thinly sliced red onions over the layered meats to add a fresh and tangy element.
Prepare the Topping: In a small bowl, mix together the melted butter, Italian seasoning, garlic powder, and onion powder. Mix thoroughly until a smooth and uniform consistency is achieved. Using a pastry brush, generously spread the butter mixture over the tops of the slider buns. This step will give the sliders a golden, flavorful crust during baking.
Bake the Sliders: Place the baking dish into the preheated oven. Bake the sliders for 15–20 minutes, or until the cheese is fully melted, and the tops of the buns are golden brown and slightly crisp. Be sure to monitor the sliders closely to avoid overbaking.
Add Lettuce and Dressing: Once baked, remove the sliders from the oven and let them cool for a few minutes. Carefully lift the top halves of the buns and sprinkle the shredded lettuce over the meats. Drizzle the prepared dressing evenly over the lettuce for added flavor. Replace the top halves of the buns, and your sliders are ready to serve warm.