Cut down the length of each sausage with a sharp knife and remove and discard casings.

Heat olive oil in a large saucepan set over high heat. Add sausages and onion. Cook, stirring occasionally and breaking up with a spatula, until sausage begins to brown, and onion turns translucent, 5 to 7 minutes.

Add oregano, thyme, and rosemary, and cook for 1 minute more.

Pour in marinara sauce. Pour 1 cup water into each jar to rinse out remaining sauce and add to the saucepan. Stir together and bring sauce to a simmer.

Reduce the heat to medium-low, and let simmer, stirring occasionally, for 1 hour. Taste for seasoning and adjust if needed. Turn off heat and skim any excess fat that rises to the surface.

Bring a large pot of generously salted water to a boil. Add ziti and cook for 1 or 2 minutes less than the directions on the package, about 8 minutes. Drain well and transfer into a large mixing bowl.

Carefully add the meat sauce to the ziti and stir until thoroughly combined. Let rest for 5 minutes.

Preheat the oven to 375 degrees F (190 degrees C). Grease a large casserole dish with a drizzle of olive oil.

Use a slotted spoon to transfer half of the pasta and sauce mixture to the prepared dish, then even out into a uniform layer. Top with half of the ricotta cheese, half of the mozzarella cheese, and then half of the Pecorino Romano cheese. Top with the rest of the pasta and sauce mixture and repeat the cheese application.

Bake in the center of the preheated oven until the cheese is melted and the casserole is piping hot, 30 to 35 minutes.