- Preheat oven to 375°F (190°C). 
- In a large saucepan, heat olive oil over medium heat. Add chopped onion and minced garlic, cook until softened. 
- Add ground beef, cook until browned. Stir in marinara sauce, salt, pepper, and oregano. Simmer for 10 minutes. 
- Cook lasagna noodles according to package instructions. Drain and set aside. 
- In a mixing bowl, combine ricotta cheese, 1 cup mozzarella cheese, and ¼ cup Parmesan cheese. 
- In a baking dish, spread a thin layer of meat sauce. Layer with noodles, ricotta mixture, and meat sauce. Repeat layers, ending with meat sauce. Top with remaining mozzarella and Parmesan cheese. 
- Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 25 minutes, until cheese is golden and bubbly. 
- Let lasagna rest for 10 minutes before serving.