Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease.

In a large bowl, combine ground beef, ground pork, breadcrumbs, Parmesan cheese, chopped parsley, minced garlic, egg, salt, pepper, dried oregano, and red pepper flakes. Mix until well combined but do not overmix.

Roll the meat mixture into 2.5-inch balls and place them on the prepared baking sheet. Bake in the preheated oven for 20-25 minutes or until they're browned and cooked through.

While the meatballs are baking, prepare the marinara sauce. In a saucepan, heat olive oil over medium heat. Add the diced onion and cook until translucent, about 5 minutes. Add the minced garlic and cook for an additional minute.

Add the crushed tomatoes, sugar, salt, pepper, dried basil, and oregano to the saucepan. Bring to a simmer and cook for 10-15 minutes, stirring occasionally.

Once the meatballs are done, remove them from the oven and reduce the temperature to 350°F (175°C).

In an oven-proof dish, spread a layer of the marinara sauce. Place the baked meatballs on top of the sauce.

Spoon some marinara sauce over each meatball, then top with the shredded mozzarella and Italian cheese blend.

Return the dish to the oven and bake for another 5-10 minutes, or until the cheese is melted and bubbly.

While the cheese is melting, toast 1/4 cup of Italian breadcrumbs in a dry pan over medium heat until golden brown, stirring frequently to prevent burning.

Remove the meatballs from the oven, sprinkle with toasted breadcrumbs and chopped fresh parsley.

Serve hot as an appetizer and enjoy your homemade Copycat Olive Garden Meatballs Parmigiana!