01 - Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
02 - In a large bowl, thoroughly combine the ground turkey, breadcrumbs, egg, milk, chopped parsley, minced garlic, grated onion, Parmesan cheese, dried oregano, salt, and black pepper. Mix gently until just combined; avoid overworking the mixture.
03 - Shape the prepared mixture into 16 to 18 meatballs, each approximately 1.5 inches in diameter. Arrange them evenly on the lined baking sheet.
04 - Bake the meatballs for 15 to 18 minutes, or until they are lightly browned and cooked through.
05 - While the meatballs are baking, heat olive oil in a large skillet or saucepan over medium heat. Add the finely diced onion and sauté for 3 to 4 minutes until it becomes translucent.
06 - Stir in the minced garlic and cook for 1 minute until fragrant. Incorporate the tomato paste and continue to cook for an additional minute.
07 - Pour in the crushed tomatoes, dried basil, dried oregano, red pepper flakes (if using), and sugar. Season with salt and black pepper to taste. Bring the sauce to a gentle simmer and cook uncovered for 15 to 20 minutes, stirring occasionally, to allow the flavors to deepen.
08 - Carefully add the baked meatballs to the simmering marinara sauce. Cover the skillet and continue to cook for 10 minutes, ensuring the meatballs are fully infused with the sauce's flavors.
09 - Garnish with fresh basil leaves before serving. These meatballs are excellent over pasta, rice, or with crusty bread.