Preheat oven to 425℉.
Cook garlic read with spread side up on a baking sheet in the preheated oven until warm and golden brown, 10-12 minutes. Set aside to cool.
Reduce oven temperature to 350℉.
In a large pot, bring spaghetti sauce to a boil. Add 30-40 frozen meatballs, reduce heat to low, and simmer until meatballs are heated through, about 20 minutes.
Tear garlic bread into bite-size pieces and spread into bottom of a 13x9-inch baking dish.
Pour spaghetti sauce and meatballs over garlic bread, coating bread with sauce and distributing meatballs evenly.
Spread Italian blend shredded cheese over top in a layer, followed by a layer of Parmesan cheese.
Bake casserole until cheese has melted, 20-25 minutes.