How to Make It
Preheat the oven to 375°F.
In a large heavy pot, heat the olive oil over medium high heat until hot then stir in the onion, garlic, 1 teaspoon salt and 3/4 teaspoon pepper and cook, stirring occasionally, until golden, about 6 minutes. Stir in the beef, breaking up the lumps of beef with a spatula and cook, until browned, about 6 minutes. Stir in the tomato paste and cook, stirring, 3 minutes. Stir in the tomatoes with their juice and the oregano, and boil, breaking up the tomatoes with a spatula until the sauce is slightly thickened, about 10 minutes. Remove the sauce from the heat and season with salt and pepper to taste.
Top with another layer of 3 noodles, then sauce, then the remaining 3 noodles and sauce. Dollop with the remaining ricotta and sprinkle with the remaining mozzarella.
Cover the lasagna dish with aluminum foil and bake until the filling is bubbling, about 45 minutes. Uncover the dish and continue to bake until the cheese is browned in places, about 30 minutes more. Let the lasagna stand 10 minutes before serving.