Flavorful marinara, tender meatballs, and a blanket of melted mozzarella cheese bake up into a comforting casserole everyone will love.
Lightly coat a baking dish with cooking spray.
Pour half a jar of marinara sauce into the bottom of the prepared baking dish and spread it into an even layer with a spoon.
Grate mozzarella cheese on the large holes of a box grater and set aside.
Grate onion on the large holes of a box grater directly into the bowl. Add minced garlic, chopped fresh parsley leaves, and grated Parmesan cheese.
Add ground beef, plain breadcrumbs, egg, Italian seasoning, salt, and pepper to the bowl. Gently mix with your hands until combined.
Form the mixture into meatballs and arrange the meatballs in a single layer nestled in the sauce as they are made.
Spoon sauce evenly over the tops of the meatballs and sprinkle the mozzarella cheese evenly over the top.
Bake at 350°F until the cheese is lightly browned and the meatballs are cooked through. about 35 to 40 minutes. Garnish with parsley.