In a large, heavy skillet over medium heat, add the oil and lightly brown the ground beef and sausage. Be sure to keep the meat chunky, not finely separated, while cooking. Add the pepperoni, tomatoes, tomato paste, oregano, salt, pepper, garlic, onion and 2 cups water. Bring to a simmer and simmer, uncovered, for 30 minutes.
Preheat the oven to 350 degrees F.
Bring a pot of water to a boil. Cook the lasagna noodles according to the package directions and drain.
In the bottom of a 9-by-13-by-2-inch baking pan, spread a layer of the prepared sauce. Top with a layer of the lasagna noodles and the ricotta, mozzarella and Parmesan cheeses. Repeat, ending with the sauce, noodles and cheeses.
Bake until lightly browned and bubbling, about 40 minutes. Allow the dish to stand for 15 minutes before serving. Cut the lasagna into 3-inch squares and serve.