01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a mixing bowl, combine ground turkey, breadcrumbs, parmesan, egg, garlic, parsley, oregano, salt, and pepper. Mix until just combined to avoid overmixing.
03 - Shape the mixture into 16 small meatballs approximately 1.5 inches each and place them on the prepared baking sheet.
04 - Bake for 15 minutes, or until lightly browned and cooked through.
05 - Heat olive oil in a large skillet over medium heat. Add onion and sauté for 2-3 minutes until softened. Add garlic and cook 1 minute more.
06 - Pour in marinara sauce and bring to a gentle simmer. Add the baked meatballs to the sauce, coating them well. Simmer uncovered for 10 minutes.
07 - Slice sub rolls lengthwise without cutting all the way through. Toast them in the oven for 2-3 minutes until lightly crisp.
08 - Divide meatballs and sauce among the rolls. Top each sub with mozzarella and a sprinkle of parmesan.
09 - Place the filled subs on a baking tray and return to the oven for 3-5 minutes, or until the cheese is melted and bubbly.
10 - Garnish with fresh basil or parsley if desired. Serve hot.