Preheat the oven to 375°F (190°C).
Cook the penne pasta in a large pot of salted boiling water according to package instructions until al dente. Drain and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat.
Add the Italian turkey sausage to the skillet, breaking it up with a spoon, and cook until browned and cooked through, about 6-8 minutes.
Add the chopped onion to the skillet and cook until softened, about 4 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the marinara sauce, diced tomatoes, dried oregano, dried basil, crushed red pepper flakes, salt, and black pepper to the skillet. Stir well to combine and simmer for 5 minutes.
In a large mixing bowl, combine the cooked pasta and the sausage tomato sauce mixture. Stir in the ricotta cheese until evenly distributed.
Transfer half of the pasta mixture into a 9×13-inch baking dish.
Sprinkle half of the shredded mozzarella and grated Parmesan cheese over the pasta layer.
Add the remaining pasta mixture on top and then sprinkle with the remaining mozzarella and Parmesan cheeses.
Cover the baking dish tightly with aluminum foil.
At this point, you can refrigerate the dish for up to 24 hours if making ahead.
When ready to bake, place the covered dish in the preheated oven and bake for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let the pasta bake rest for 5 minutes.
Garnish with chopped fresh parsley before serving.