Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.

Bring salted water to a boil. Cook manicotti shells for 6-8 minutes until al dente, then drain and rinse under cold water.

In a large skillet, cook ground beef and Italian sausage over medium heat for 6-8 minutes until browned. Drain fat, then add onion and garlic, sauté for 3-4 minutes.

Add oregano, basil, salt, and pepper to the skillet, stir to combine, and cook for another minute then set aside to cool.

In a mixing bowl, combine ricotta, 1 cup of mozzarella, Parmesan, and beaten egg. Fold in the cooled meat mixture.

Carefully fill manicotti shells with the creamy filling using a piping bag or spoon.

Arrange filled manicotti in the baking dish and cover with marinara sauce.

Sprinkle remaining mozzarella cheese on top.

Cover with foil and bake for 25 minutes, then remove foil and bake for an additional 10-15 minutes until cheese is golden and bubbly.

Let rest for 5 minutes, garnish with parsley, and serve warm.