01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, combine ground turkey, breadcrumbs, Parmesan, egg, garlic, parsley, oregano, salt, pepper, and milk. Mix gently until just combined to avoid tough meatballs.
03 - Shape the mixture into sixteen 1.5-inch meatballs. Place them evenly on the prepared baking sheet and bake for 15 to 18 minutes until golden and cooked through.
04 - While the meatballs bake, heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 3 to 4 minutes. Stir in garlic and sauté for an additional minute.
05 - Add crushed tomatoes, dried basil, oregano, sugar, salt, and pepper to the skillet. Simmer gently for 8 to 10 minutes, stirring occasionally.
06 - Transfer the baked meatballs into the simmering sauce and continue cooking for 5 to 7 minutes, spooning the sauce over the meatballs to infuse flavor.
07 - Preheat the broiler. Split the sub rolls and place them cut side up on a baking sheet. Toast under the broiler for 1 to 2 minutes until lightly browned.
08 - Place four meatballs with sauce on each toasted roll. Top evenly with shredded mozzarella and a sprinkle of Parmesan cheese.
09 - Broil the assembled subs for 2 to 3 minutes until the cheese is melted and bubbly. Garnish with fresh basil if desired and serve immediately.