01 - Preheat oven to 400°F and line a baking sheet with parchment paper.
02 - In a large bowl, gently mix ground turkey, breadcrumbs, Parmesan, egg, milk, garlic, parsley, oregano, salt, and pepper until just combined.
03 - Form mixture into 16 small meatballs, approximately 1.5 inches each, and arrange evenly on the baking sheet. Bake for 15 to 18 minutes until lightly browned and cooked through.
04 - While meatballs bake, heat olive oil in a large skillet over medium heat. Add marinara sauce and red pepper flakes, bring to a simmer.
05 - Add baked meatballs to the simmering sauce and cook for 10 minutes, turning occasionally to ensure even coating.
06 - Preheat broiler. Split sub rolls and toast lightly if desired.
07 - Place 4 meatballs with sauce into each roll, then top with mozzarella and Parmesan cheese.
08 - Place assembled subs under the broiler for 1 to 2 minutes until cheese is melted and bubbly.
09 - Garnish with fresh basil leaves if desired, and serve immediately.