Make the meatballs: Preheat the broiler. In a large mixing bowl, whisk together the eggs, pecorino, parsley, garlic and some salt and pepper until it is all incorporated. Add the ground meats and breadcrumbs and, using your God-given hands, get after it and mix away. Do not overwork the meat or it will turn meatloaf-y. You want it loose and supple.
Using your hands again, make 6 loose patties to match the size of your bread. Heat some oil in a large heavy-bottomed cast-iron pan (or use a griddle pan) over medium heat. In batches, fry the patties until golden brown, 4 to 5 minutes per side. Transfer to a baking sheet.
For the sandwich build: Toast the split buns under the broiler, about 3 minutes. Spoon 3 tablespoons of sauce on top of each patty and top with a few slices of mozzarella. Place the patties under the broiler until melted and golden, 3 to 5 minutes. Place the patties on the buns and top with giardiniera and roasted red peppers. Cut in half and serve with the remaining marinara sauce on the side.
Photograph by Ryan Liebe