Preheat the oven to 375°F (190°C).
Cook the penne pasta according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium heat.
Add the diced onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground turkey to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 6-8 minutes.
Stir in the marinara sauce, dried Italian seasoning, salt, black pepper, and crushed red pepper flakes. Simmer for 5 minutes.
In a large mixing bowl, combine the cooked pasta, turkey tomato sauce mixture, ricotta cheese, and half of the shredded mozzarella cheese. Mix until well combined.
Transfer the mixture to a 9×13-inch baking dish.
Sprinkle the remaining mozzarella cheese and the grated Parmesan cheese evenly over the top.
Bake uncovered in the preheated oven for 20 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it rest for 5 minutes.
Garnish with chopped fresh parsley before serving.