Add all of the meatball ingredients except the oil and mix to combine. Roll into meatballs (size is your preference) — note that larger meatballs will take longer to cook through.
Place a pan over medium-high heat, add the olive oil, and sear the meatballs for 5–6 minutes, rotating frequently until browned on all sides. Remove and set aside.
Add the onion to the same pan and sauté for 3–4 minutes, until slightly translucent. Add the garlic and cook for 1 minute.
Add the crushed or diced tomatoes, a splash of water to rinse the can, tomato passata, basil, and a good seasoning of salt and pepper. Bring to a boil, reduce the heat to low, and simmer for 15–20 minutes. Add a pinch of sugar here if you like.
Return the meatballs and any resting juices to the sauce and cook for 6–8 minutes, or until the internal temperature of the meatballs reaches 71°C (160°F). Check and adjust the seasoning.
Preheat the oven to 200°C (390°F) on the grill/broiler setting.
Slice the rolls and lather with butter or extra virgin olive oil. Spread with basil pesto, top with sliced mozzarella, and place under the grill to toast and melt. Use a blowtorch to finish the cheese if needed.
Place the meatballs on the other side of the toasted roll and top with marinara sauce, freshly grated Parmigiano Reggiano, basil leaves, and cracked black pepper. Close the roll, slice, and dig in.