Cook the pasta:
Preheat the oven to 375°F (190°C). Cook the pasta in a large pot of salted boiling water according to package instructions, until al dente. Drain and set aside.
Brown the sausage:
In a skillet over medium heat, brown the Italian sausage until fully cooked, breaking it up with a wooden spoon. Drain any excess fat and stir in the marinara sauce. Season with salt, pepper, and Italian seasoning. Simmer for 5 minutes.
Prepare the cheese mixture:
In a mixing bowl, combine the ricotta cheese, 1 cup of mozzarella, Parmesan cheese, garlic powder, and a pinch of salt and pepper. Mix until smooth.
Assemble the casserole:
In a 9x13-inch baking dish, spread a thin layer of the sausage and marinara mixture on the bottom. Add a layer of cooked pasta, followed by dollops of the ricotta cheese mixture. Repeat with another layer of sauce, pasta, and ricotta, finishing with a final layer of sauce. Sprinkle the remaining 1 cup of mozzarella on top.
Bake:
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is golden and bubbly.
Serve:
Let the casserole rest for 5 minutes before serving. Garnish with fresh basil or parsley if desired.