Preheat oven to 350℉. Coat a 9 x 13 baking dish with nonstick cooking spray.
Cut slider buns in half crosswise through the middle to separate the tops from the bottoms. Place bottom halves in the baking dish.
Spread marinara sauce onto buns and sprinkle with 1 tsp Italian seasoning. Add layers of salami, prosciutto, pepperoni, and cheese. Then, add the top half of the slider buns.
Melt the butter in the microwave in a small bowl or in a small saucepan over medium heat. Add remaining Italian seasoning and Italian salad dressing (if using). Use a basting brush to brush the butter mixture on top of buns.
Cover baking dish with aluminum foil and bake 20-30 minutes, until cheese begins to melt and the butter absorbs into rolls.
Slice into individual sandwiches and serve.
Notes
Serve with Italian dressing or marinara sauce for dipping, if desired.