In a large mixing bowl, combine the ground turkey, breadcrumbs, grated Parmesan, chopped fresh parsley, minced garlic, salt, black pepper, and the egg. Mix gently until just combined.
Form the mixture into 1 to 1.5-inch meatballs, about the size of a golf ball, making approximately 16 meatballs. Place on a clean plate or tray.
Heat olive oil in a large skillet over medium heat. Add the meatballs carefully without overcrowding. Brown on all sides for about 5-7 minutes total, turning gently.
Pour the jar of marinara sauce over the browned meatballs. Nestle meatballs gently into the sauce. Reduce heat to low, cover, and simmer for 15-20 minutes.
Remove lid and sprinkle shredded mozzarella evenly over meatballs and sauce. Cover again and cook for a few minutes until cheese is melted and bubbly.
Scoop meatballs and sauce onto plates or serve family-style from the skillet. Enjoy with pasta, crusty bread, or salad.