Brown the sausage in a large skillet over medium heat, cooking until it develops crispy edges and releases its flavor.
Add the diced onion to the skillet and sauté until it becomes soft and translucent, blending with the sausage.
Stir in the tomato paste, crushed tomatoes, Italian seasoning, and water, then bring the mixture to a simmer and let it cook gently while flavors develop.
Cook the ziti in salted boiling water until tender but still firm, then drain well to prevent excess moisture in the dish.
In a separate bowl, mix the ricotta, Italian cheese blend, and black pepper until smooth and well combined.
Return the drained pasta to the pot and toss it with a portion of the sauce to coat it evenly before layering.
Layer half of the pasta in a baking dish, followed by dollops of the ricotta mixture and a portion of the sauce, then repeat the layers evenly.
Top with shredded mozzarella, cover loosely with foil, and bake until heated through and the cheese begins to melt.
Remove the foil and broil briefly until the cheese turns golden and bubbly, watching closely to avoid burning.
Garnish with parsley if desired and serve warm while the cheese is still melty.
