Heat a large skillet over medium heat. Add the ground beef and Italian sausage. Cook until browned, breaking it apart with a spoon.
Add the chopped onion and minced garlic, cooking until softened and fragrant.
Stir in the marinara sauce and let it simmer for 10-15 minutes to combine the flavors. Season with salt, pepper, and Italian seasoning.
In a bowl, combine the ricotta cheese, beaten egg, and Parmesan cheese. Season with salt and pepper.
Preheat your oven to 375°F (190°C).
Spread a thin layer of meat sauce in the bottom of a 9x13-inch baking dish.
Layer the cooked lasagna noodles on top, then add a layer of the ricotta mixture, followed by a generous layer of meat sauce. Sprinkle with shredded mozzarella cheese.
Repeat the layering process until all ingredients are used, finishing with a layer of mozzarella cheese on top.
Cover with foil and bake for 25 minutes. Remove the foil and bake for an additional 15-20 minutes, until the cheese is melted and golden.
Let the lasagna rest for 10-15 minutes before slicing. Serve and enjoy!