Preheat your oven to 375°F (190°C).

Bring a large pot of salted water to a boil. Add the cheese tortellini and cook according to package instructions until al dente, about 3-5 minutes. Drain and set aside.

In a large mixing bowl, combine the marinara sauce, ricotta cheese, Italian seasoning, salt, and pepper. Stir until well blended.

Add the cooked tortellini to the sauce mixture and gently fold until every piece is coated.

In a greased 9x13-inch baking dish, spread half of the tortellini mixture evenly across the bottom. Sprinkle half of the shredded mozzarella cheese on top. Layer the remaining tortellini mixture over this, followed by the rest of the mozzarella and the grated Parmesan cheese.

Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.

Let the casserole cool for a few minutes before serving. Garnish with fresh basil leaves if desired.