Bring a large pot of salted water to a boil, then add the ziti pasta, cooking until al dente according to package instructions, usually about 8-10 minutes. Once cooked, drain the pasta and toss it with a splash of olive oil to prevent sticking, letting it sit while you prepare the sauce.

In a medium saucepan over medium heat, combine the marinara sauce, heavy cream, and diced tomatoes, then add a pinch of sugar to balance acidity. Stir to mix, and bring the sauce to a gentle simmer. Once heated, add half of the Parmesan, fontina, and mozzarella cheeses, stirring until melted and smooth.

Grease a 9x13-inch baking dish with cooking spray or butter for easy cleanup. Layer the cooked ziti evenly in the dish, pouring the creamy Cheese Ziti Al Forno sauce over it, ensuring every piece is covered. Sprinkle the remaining cheeses and breadcrumbs on top.

Preheat your oven to 350°F (175°C). Cover the baking dish with aluminum foil and bake for 30-45 minutes, or until the edges bubble and the center is heated through. For a golden, crispy top, remove the foil and broil on high for an additional 2-3 minutes.

Once out of the oven, let the Cheese Ziti Al Forno sit for a few minutes to set before serving. Garnish with freshly grated Parmesan cheese.