Lasagna Style Baked Ziti

1 pound ziti
1 tablespoon olive oil
1 large yellow onion, diced
3/4 teaspoon kosher salt
1/4 teaspoon black pepper
1 pound lean ground beef
3 cloves garlic, minced
1/2 cup chopped fresh oregano (optional)
1 26-ounce jar pasta sauce
1/2 cup (2 ounces) grated Parmesan
1 15-ounce container ricotta
1 10-ounce box frozen spinach, thawed and squeezed to remove liquid
1 cup grated mozzarella

Cook the ziti according to the package instructions.

Heat oven to 400° F.

In a large pot, over medium-low heat, heat the oil. Add the onion, salt, and pepper. Cover and cook until the onion is softened, 5 to 7 minutes. Add the beef, increase heat to medium-high, and cook until no trace of pink remains, 5 to 8 minutes. Drain any remaining liquid. Add the garlic and oregano (if using) and cook for 2 minutes. Add the pasta sauce and heat for 3 minutes. Remove from heat. Add the cooked pasta and toss to coat. Add the Parmesan, ricotta, and spinach and toss again. Spread the mixture into a 9-by-13-inch baking dish or individual ramekins and sprinkle with the mozzarella. Bake until the mozzarella melts, about 15 minutes.