Top-ranked recipe named "Lasagna-Style Baked Ziti"
1. Cook ziti according to the package instructions.
2. Heat oven to 400.
3. In a large pot, over med-low heat, heat the oil. Add onion, salt & pepper. Cover & cook until the onion is softened, 5-7 minutes. Add the beef, increase heat to med-high, and cook until no trace of pink remains, 5-8 minutes. Drain any remaining liquid.
4. Add the garlic & oregano (if using) and cook for 2 minutes. Add the pasta sauce & heat for 3 minutes. Remove from heat. Add the cooked pasta and toss to coat.
5. Add the parmesan, ricotta & spinach and toss again. Spread the mixture into a 9x13 inch baking dish or individual ramekins and sprinkle with the mozzarella.
6. Bake until the mozzarella melts, about 15 minutes.