Preheat oven to 375℉. Spray a 9x13 pan with cooking spray.
Place the olives, giardiniera mix, oregano, garlic, red onion, red wine vinegar and olive oil in the bowl of a food processor. Pulse 5-6 times until all of the ingredients are uniformly chopped. Set aside.
Using a large serrated knife, slice the rolls in half so you have a “slab” of tops and a “slab” of bottoms; don’t pull the rolls apart and slice individually because you want to keep them connected. Hold the top with one hand to keep them steady.
Place the bottom half of the slider buns in the prepared dish and bake for 5 minutes until just beginning to toast.
In a small bowl mix together the melted butter and minced garlic, set aside.
Start layering the sandwich with mortadella, ham, salami and provolone. Using a slotted spoon, layer the olive salad over the cheese. Be sure to let the liquid drain off as much as possible with each scoop.
Place the top half of the rolls on top of the olive mixture. Brush with the garlic butter and sprinkle with sesame seeds.
Cover loosely with foil and bake for 15 minutes. Remove foil and bake for another 5 minutes until the top is lightly browned.
Let cool for 5 minutes, then cut the sliders apart and serve immediately.
Notes
Sliders are best the day they are made, as they tend to get soggy as they sit. Any leftovers should be wrapped tightly in plastic wrap and stored in the refrigerator for up to 3 days.