Preheat oven to 300F, line a baking sheet with parchment.  

In a food processor, combine the mayonnaise, jarred peppadew peppers and brine. Pulse until completely combined. Set aside.

Slice the baguettes in half. Spread about 2 tablespoons or more of the peppadew mayo on the cut side of the baguettes to coat completely. Slice the provolone cheese slices in half then layer them over each baguette half, making sure they’re covered with cheese. Place the bread cheese-side-up on the baking sheet and cook until the cheese has completely melted and is starting to bubble, about 10 minutes. 

Remove from the oven and carefully layer the mortadella, pepperoni and salami over the bottom half of each of the baguettes, dividing the meat evenly. Return to the oven and bake until the cold meats are warm, for 1 to 2  minutes. Remove from the oven. 

Place about 1/2 cup of arugula on top of the sliced meats. Garnish with Marinated Red Onions and some of the onion oil. Put the top half of the baguettes, cheese-side-down, on top of the assembled sandwich. Slice the sandwiches in half to serve. Enjoy with extra peppadew mayo on the side.