Prep the ingredients per the instructions above.
Place the sauce in a pot over medium low heat. Cover with a lid and bring to a low simmer.
Make the meatballs: Heat half of the oil in a saute pan over medium heat. Saute the onion and garlic until softened and lightly golden brown. Set aside. In a bowl, mix together the bread and milk. Let sit for 2 to 3 minutes until the bread is soggy. Mix in the ground beef, oregano, onion, garlic, parmesan, and season with salt and pepper. Mix until well combined. Using your hands, form the meat into equally-sized balls.
Heat the remaining oil in a saute pan over medium heat. Sear the meatballs all around until nicely browned all over, work in batches if needed so as to not crowd the pan. Then place the meatballs into the sauce and cover with a lid. Simmer the meatballs to an internal temperature of 160 °F (71 °C) using a thermometer.
Preheat the oven broiler on low.
Prep the roll: Place on a baking sheet. Lightly toast under the broiler.
Place the meatballs on the sub roll, spoon on some of the sauce, and then top with cheese. Place under the broiler until the cheese is melted and bubbly.
Cut the sandwich in half and serve with chips and sparkling water.