01 - Preheat oven to 375°F and line a baking sheet with parchment paper.
02 - Combine ground turkey, breadcrumbs, Parmesan, egg, garlic, parsley, oregano, salt, and pepper in a large bowl; mix until just combined.
03 - Shape mixture into 12-16 meatballs about 1 1/2 inches in diameter and place on prepared baking sheet. Bake for 18-20 minutes until cooked through and lightly browned.
04 - Heat olive oil in a large skillet over medium heat, cook onion until soft, about 3 minutes. Stir in garlic and red pepper flakes, cooking for 30 seconds.
05 - Add marinara sauce and dried basil to skillet and simmer for 5 minutes.
06 - Transfer baked meatballs into the sauce and simmer for 5-7 minutes, spooning sauce over meatballs to coat thoroughly.
07 - Slice rolls without cutting through completely. Place 3-4 meatballs with sauce into each roll.
08 - Top meatballs with shredded mozzarella and sprinkle Parmesan cheese. Place subs on baking sheet and broil on high for 2-3 minutes until cheese is melted and bubbly.
09 - Garnish with fresh basil or parsley if desired and serve warm.