Cover the bread entirely in cold water and let it sit for 5 to 6 minutes or until soaked and soft.
Using your hands, squeeze as much water from the bread as possible.
Add it to a large bowl with the beef, pork, Italian sausage, Parmigiano, eggs, breadcrumbs, onion and garlic granules, dry basil and oregano, bell peppers, salt, and pepper.
Mix thoroughly until all the ingredients are combined. Form them into 18 equal sized meatballs.
Add 2 tablespoons of olive oil to a large rondeau pot, heat over medium heat, and fry the meatballs until browned on both sides, about 2 to 3 minutes per side.
Set them to the side. Add the tomato puree along with 3 cups of water, Italian seasonings, crushed red pepper flakes, and salt. Cook for 10 to 12 minutes or low to medium heat.
Place the meatballs back in and cook for 10 to 12 minutes or until they are cooked through and reach 165° internally.
Next, slice the hoagie buns in half without going through, and brush the insides with some olive oil. Add them to a sheet tray lined with parchment paper and bake them on a middle rack in the oven at 425° for 5 to 7 minutes or until toasted.
Sprinkle about ¼ of shredded mozzarella to the bottom of the bun and then fill the sandwich with meatballs and sauce.
Sprinkle on an additional ¼ cup of mozzarella and bake on a middle rack at 425° for 4 to 6 minutes or until the cheese is melted.
Serve the subs with additional sauce and optional garnishes of grated parmigiano and minced parsley.
Notes
Make-Ahead: This is meant to be eaten as soon as it’s made. However, keeping the meatballs and sauce separate from the bread can be made up to two days ahead for freshness.How to Store: It is best to store the meatballs and sauce separately from the bread in the fridge for 4 days. If the sub is already made, cover and keep in the fridge for 2 days. The sandwich will not freeze well.How to Reheat: Heat the meatballs and sauce in a medium-sized pot over low heat until warm. If the sub is assembled, wrap it in foil, place it in the oven at 350°, and cook for 8 to 12 minutes or until warm.Place some small plates onto the bread to help keep it submerged.The bread for the meatball batter is about 4” to 5” thick.