Preheat oven to 375°F and spray a 9x13-inch baking dish with cooking spray.
Cook penne pasta according to package directions until just al dente. Drain and return to pot.
In a large bowl, combine ricotta cheese, beaten egg, 1 cup mozzarella, Parmesan, Italian seasoning, and garlic powder. Mix well.
Add marinara sauce to the cooked pasta and toss to coat evenly.
Spread half of the pasta mixture in the bottom of the prepared baking dish. Arrange meatballs evenly over the pasta.
Drop spoonfuls of the ricotta mixture over the meatballs, then top with remaining pasta.
Cover tightly with foil and bake for 25 minutes.
Remove foil, sprinkle remaining 1 cup mozzarella over the top, and bake uncovered for 10 more minutes until cheese is melted and bubbly.
Let stand 5 minutes, garnish with fresh parsley, and serve hot.