Preheat the oven to 350°F/180°c.
Add the olive oil and diced onion to a large skillet heated over medium-high heat. Cook, stirring often, for 4 minutes or until softened. Add the garlic and cook, stirring, for 1 minute or until fragrant.
Add the ground beef to the onion mixture and cook, stirring and breaking up lumps with the back of a wooden spoon, until the beef is no longer pink.
Add the marinara sauce and Italian seasoning to the beef mixture, and stir until well combined. Season to taste with salt and pepper. Remove from the heat.
Combine the mozzarella cheese and grated parmesan in a mixing bowl. Set aside.
Spoon ⅓ of the ground beef mixture into a 9 x 13 inch baking dish. Arrange half of the ravioli over the sauce.
Spread all of the ricotta cheese over the ravioli. Top with ½ of the remaining beef sauce, and then ½ of the shredded mozzarella cheese.
Arrange the remaining ravioli over the cheese layer, then top with the remaining beef mixture.
Cover with a sheet of foil, and bake in the oven for 20 minutes. Remove the foil and sprinkle the remaining mozzarella cheese mixture over. Return to oven, uncovered, and bake for another 10 minutes, or until the cheese is melted and golden.
Top with the fresh parsley, if using, and serve.