In a large pot of boiling salted water, cook the frozen tortellini according to package instructions until al dente. Drain and set aside.
In a mixing bowl, combine the marinara sauce, heavy cream, Italian seasoning, garlic powder, salt, and pepper. Mix well to create a creamy tomato sauce.
Gently fold the cooked tortellini into the tomato sauce mixture until well coated.
Transfer the tortellini mixture into a greased 9x13 inch baking dish, spreading it evenly.
Sprinkle the shredded mozzarella and grated Parmesan cheese over the top of the tortellini.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly, and the edges are slightly golden.
Remove from the oven and let it cool for a few minutes. Garnish with fresh basil leaves before serving.