Preheat the oven to 350β and spray a 9x13 pan with cooking spray. Set aside.
Slice the Hawaiian rolls lengthwise, leaving them connected. Place the bottom into the prepared pan.
Next, layer the pepper jack and provolone cheeses on the bottom. Then add the turkey, pepperoni, mortadella, salami, and prosciutto. Place the top of the Hawaiian rolls on top of the cheese. Brush with melted butter.
Bake the sliders for 15 minutes at 350β.
While the sliders are baking prepare the toppings. Place the sliced white onion, red wine vinegar, and dried oregano in a large bowl. Stir to combine and set aside. Let the onions marinate for 5 minutes.
After the onions have had time to sit, add the shredded lettuce and olive oil to the onions. Stir to combine. Set aside.
Add the mayonnaise and mustard to a small bowl and stir to combine.
When the sliders are done baking, take them out of the oven and transfer to a cutting board. Gently take the top off and set aside. Top the sliders with the lettuce, sliced tomatoes, and pickles. Spread the mayo mix on the top of the Hawaiian rolls.
Place the slider tops on top and cut to serve.