Heat a large skillet over medium-high heat and add the olive oil. Add the ground beef and cook until no longer pink. Add the chopped onions and cook for another 3 minutes. Break the meat into crumbles and season with salt and pepper.
According to the package instructions, cook the pasta in a large pot of salted water. Drain and set aside. Combine the cooked pasta, ricotta cheese, egg, parsley, and 1 cup mozzarella cheese in a bowl.
Transfer the mixture to a greased baking dish and top with the cooked beef. Top with the pasta sauce.
Cover the baking dish with foil and bake for 45-50 minutes. Sprinkle with the remaining mozzarella cheese and bake uncovered until the cheese is melted, about 5-10 minutes. Remove the lasagna casserole from the oven and let stand for 10 minutes before serving.