Cook the Pasta

• Bring a large pot of salted water to a boil. Cook the ziti pasta until al dente according to the package instructions. Drain and set aside.

Cook the Sausage and Onion

• Heat the olive oil in a large skillet over medium heat. Add the Italian sausage and cook, breaking it into small pieces, until browned.
• Stir in the chopped onion and cook for 5-7 minutes, or until softened. Add the minced garlic and cook for 1 minute until fragrant.

Make the Tomato Sauce

• Add the crushed tomatoes, tomato paste, oregano, red pepper flakes (if using), salt, and black pepper to the skillet. Stir well to combine.
• Simmer the sauce for 10-15 minutes to thicken slightly and allow the flavors to meld.

Combine the Pasta and Sauce

• In a large mixing bowl, combine the cooked pasta and tomato sauce. Stir until the pasta is evenly coated.

Assemble the Baked Ziti

• Preheat the oven to 375°F (190°C).
• Spread a thin layer of the pasta mixture in the bottom of a greased 9×13-inch baking dish.
• Layer half of the ricotta cheese, half of the mozzarella cheese, and half of the Parmesan cheese over the pasta.
• Add the remaining pasta mixture on top, then layer with the remaining ricotta, mozzarella, and Parmesan cheese.

Bake the Ziti

• Cover the dish with aluminum foil and bake for 20 minutes.
• Remove the foil and bake for an additional 15-20 minutes, or until the cheese is golden and bubbly.

Garnish and Serve

• Remove the baked ziti from the oven and let it rest for 5 minutes. Garnish with fresh parsley before serving.