Preheat the Oven: Preheat oven to 425°F and grease a 9x13-inch casserole dish.
Assemble Pasta Base: Add uncooked 16 ounce box penne pasta to the dish. Pour 3 cups water and 24 ounce jar pasta sauce over the pasta. Stir to fully coat.
Layer the Casserole: Add half of the meatballs evenly over the pasta, then sprinkle with half of the mozzarella cheese.
Finish Assembly: Add the remaining meatballs in neat rows or columns, then sprinkle with the rest of the mozzarella cheese.
Add Herbs and Cover: Sprinkle parsley flakes over the top. Cover the dish tightly with foil.
Bake Covered: Bake for 25 minutes.
Uncover and Finish Baking: Remove foil and bake for an additional 10 minutes, or until the cheese is melted and bubbling and pasta is tender.
Cool Slightly: Let rest for 5 minutes before serving.
Notes
Make-Ahead Tips: Assemble casserole up to one day in advance and refrigerate. Add 5 extra minutes to the bake time if starting from cold.Storage: Cover tightly or transfer leftovers to an airtight container. Refrigerate for 3 to 4 days.Freezing Instructions: Assemble but do not bake. Cover tightly with foil and freeze for up to 2 months. Bake from frozen at 375°F for 60-70 minutes or thaw overnight and bake as directed.Customization Ideas: Use your favorite jarred sauce (vodka, basil garlic, or spicy arrabbiata). Try other shredded cheeses like provolone or a cheddar blend for a fun twist.Substitutions: Swap penne for shells, elbows, or bowties. Use turkey or chicken meatballs for a leaner option.