Gather all ingredients. Slice each sausage link lengthwise and remove and discard the casings.
Heat olive oil in a large saucepan over high heat. Add sausage and onion. Cook, breaking up with a spatula, until sausage browns and onion turns translucent, 5 to 7 minutes. Add oregano, thyme, and rosemary and cook 1 minute more.
Pour in marinara sauce. Add 1 cup of water to each empty jar, swirl, and pour into the pan. Stir and bring to a simmer.
Reduce heat to medium-low and simmer for 1 hour, stirring occasionally. Taste and adjust seasoning. Turn off heat and skim any excess fat from the surface.
Bring a large pot of salted water to a boil. Cook ziti 1 to 2 minutes less than package directions, about 8 minutes. Drain well and transfer to a large mixing bowl.
Add meat sauce to pasta and stir to combine. Rest 5 minutes. Preheat oven to 375°F (190°C). Grease a 9x15-inch casserole dish with olive oil.
Spoon half the pasta mixture into the dish and spread evenly. Top with half the ricotta, half the mozzarella, and half the Pecorino Romano. Add remaining pasta, shake pan gently to settle, then repeat the cheese layers.
Bake 30 to 35 minutes until cheese is melted and bubbling. Rest 10 to 15 minutes before serving. Top with fresh parsley.