First, you'll prepare the meatballs. In a large bowl, place the beef, chopped onion, beaten egg, and breadcrumbs. Mix until all ingredients are well combined.
Heat a frying pan to medium-high heat, and pour 1/4 cup of cooking oil in it. Roll a tablespoon of the mixture into a ball and place each meatball on the frying pan. Cook the meatballs in batches until they turn brown on all sides.
In a saucepan, heat up your marinara sauce with all the spices until hot. Divide the sauce in half. Add the meatballs to one half of the marinara sauce and coat them completely. The other half will be used to pour over the sub in the next step.
Take your baguettes and slice them in half, length-wise. Place 3 or 4 meatballs inside, and gently drizzle some of the other half of marinara sauce over the meatballs. Sprinkle grated cheese over the meatballs and sauce, and close the sub. Serve hot.