Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish or line it with parchment paper.

Slice the slider buns horizontally, keeping the top and bottom halves intact as a sheet. Place the bottom halves in the prepared baking dish.

In a small bowl, mix the melted butter, garlic powder, Italian seasoning, and Dijon mustard. Set aside.

Spread a thin layer of mayonnaise and marinara sauce over the bottom halves of the buns.

Layer the halal turkey pastrami, beef bologna, and chicken mortadella evenly over the buns. Follow with the provolone and mozzarella slices.

Sprinkle the sliced banana peppers and black olives evenly over the cheese layer.

Place the top halves of the slider buns over the layered fillings.

Brush the tops of the buns generously with the butter mixture. Sprinkle grated Parmesan cheese over the tops, if using.

Cover the baking dish with aluminum foil and bake in the preheated oven for 15 minutes.

Remove the foil and bake for another 5-7 minutes, or until the tops are golden brown and the cheese is melted and bubbly.

Carefully remove the sliders from the oven and let them cool for a few minutes before slicing and serving.