Preheat the oven to 350 degrees F. In a large pot of boiling, salted water, cook the manicotti tubes according to package directions. Drain
, rinse in cold water, and pat dry. In a nonstick skillet set over moderate heat, warm the oil until hot. Add the onion and cook it, stirring occasionally, for 5 minutes. Add the meat, lemon pepper, oregano, salt, and pepper, and cook, stirring, until the meat is no longer pink. Transfer the meat to a bowl, add the parsley, tomatoes, ricotta, and half the Parmesan
, and fill the pasta tubes with the meat mixture. Spoon 1 cup sauce in bottom of shallow baking dish
, top with the filled pasta
tubes, and spoon the remaining sauce over them. Sprinkle with Parmesan and bake for 25 to 30 minutes, or until sauce is bubbling.