Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Drain well and set aside.
In a large skillet, heat the olive oil over medium heat. Add the minced garlic and red pepper flakes, sautéing for about 1-2 minutes until fragrant, but not browned.
Stir in the drained diced tomatoes and shredded cooked chicken. Cook for 3-4 minutes until heated through and the flavors meld. Season lightly with salt, pepper, and the dried oregano.
In a mixing bowl, combine the ricotta cheese, shredded mozzarella, and half of the grated Parmesan.
Add the cooked penne pasta to the skillet with the tomato and chicken mixture. Stir in the cheese mixture until everything is evenly combined.
Transfer the pasta mixture to a greased 9x13-inch baking dish. Sprinkle the remaining Parmesan cheese evenly on top.
Bake in a preheated 375°F (190°C) oven for about 20 minutes or until the cheese on top is melted and bubbly with a light golden color.
Remove from the oven and sprinkle with freshly chopped parsley. Serve hot and enjoy.