Combine ground chicken, breadcrumbs, Parmesan cheese, parsley, garlic, onion powder, Italian seasoning, salt, black pepper, and egg in a large mixing bowl. Mix until well combined.
Shape the mixture into meatballs about 1.5 inches in diameter and place on a baking sheet lined with parchment paper.
Preheat oven to 400°F and bake meatballs for 20 minutes until cooked through and golden brown.
Prepare marinara sauce by heating store-bought or homemade sauce in a saucepan.
Spoon warm marinara sauce over meatballs, sprinkle with mozzarella cheese, and return to oven for an additional 5-7 minutes until cheese is melted.