01 - Preheat 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 integrated without overmixing.
03 - Shape mixture into 16 meatballs, approximately 1 1/2 inches in diameter. Arrange on the prepared baking sheet and bake for 15 minutes until lightly browned and fully cooked.
04 - Heat olive oil in a large skillet over medium heat. Sauté onion until softened, about 2-3 minutes, then add garlic and cook for an additional minute.
05 - Add marinara sauce to the skillet and bring to a gentle simmer. Incorporate baked meatballs, coating them thoroughly with the sauce. Simmer uncovered for 10 minutes.
06 - Slice sub rolls lengthwise without cutting through. Place in the oven and toast for 2-3 minutes until lightly crisp.
07 - Distribute meatballs and sauce evenly among the toasted rolls. Top each with shredded mozzarella and a sprinkle of parmesan cheese.
08 - Place the assembled subs on a baking tray and bake for 3-5 minutes until cheese is melted and bubbly. Optionally garnish with fresh basil or parsley before serving.