Heat a drizzle of olive oil in a large skillet or saucepan over medium heat.

Add the chopped onion, bell pepper, and kosher salt. Sauté for 4–5 minutes, or until the onion becomes translucent and the vegetables begin to soften.

Add the minced garlic and cook for another minute, stirring frequently.

2. Make the Tomato Sauce

Add the diced tomatoes to the skillet.

Cook over medium heat for about 15 minutes, stirring occasionally, until the sauce thickens.

Season with pepper to taste.

3. Cook the Pasta

While the sauce cooks, prepare the ziti according to the package directions, stopping about 2 minutes before the recommended cooking time.

The pasta should be firm but not hard. It will continue cooking in the oven.

Drain thoroughly.

4. Combine the Pasta and Cheese

Preheat the oven to 350°F.

In a large bowl or pot, combine the tomato sauce, cooked ziti, Parmesan cheese, and 1½ cups of mozzarella.

Stir until the pasta is evenly coated and the cheese is distributed throughout.

5. Assemble the Casserole

Lightly grease a 9 × 11-inch casserole dish with olive oil.

Transfer the pasta mixture into the dish and spread it evenly.

Sprinkle the remaining ½ cup mozzarella over the top.

6. Bake

Bake uncovered for 30 minutes, or until the cheese is golden, melted, and bubbly.

Let the baked ziti rest for a few minutes before serving.