Pour the tomatoes into a bowl and crush them up with your hands. Pour 1 cup water into the can and slosh it around to get the tomato juices and set aside.
Heat the oil in a skillet or sauté pan over medium heat, once the oil is hot, add the garlic and basil stems. Sauté for 1-2 minutes until the garlic just starts to become golden brown. Stir in tomatoes and water from the can, season generously with salt, bring to a simmer for 20-25 minutes.
In the meantime, mix together the breadcrumbs, milk, ground beef, and season with salt and pepper. Mix until well combined. Using your hands, form the meat into bite-sized balls (dampen your hands with water to prevent the meat from sticking).
Heat a non-stick pan over medium heat. Add the meatballs in batches without crowding the pan and sauté until nicely browned all over.
Cook meatballs in the sauce, turning occasionally, to an internal temperature of 160°F using a thermometer.
Toast the sub roll to golden brown under the oven broiler on low.
Taste the sauce and adjust the seasoning with salt as needed. Once the majority of the liquid has evaporated, remove from the heat and stir in the basil; top the meatballs with cheese and place under the broiler to melt.
Portion the meatballs onto the rolls along with a few spoonfuls of sauce, cut in half and serve with chips (be careful not to over sauce the sandwich). Freeze any remaining sauce for future use in a tightly sealed container.