Combine the ground chuck and beef in a large mixing bowl. Add the bread crumbs, eggs, grated cheeses, minced garlic, chopped parsley, and red pepper flakes. Mix the ingredients by hand until the mixture is cohesive but not overly compressed.

Shape the mixture into evenly sized meatballs, each about 1 1/2 inches in diameter. Generously season all sides of the meatballs with kosher salt and freshly cracked black pepper.

If using a charcoal grill, ignite a full chimney of charcoal. Once the coals are fully lit and covered in a layer of ash, spread them out across the grill’s base. For gas grills, turn all burners to high heat. Place the cooking grate over the heat source, close the lid, and allow it to preheat for about 5 minutes.

Carefully clean and oil the grill grates. Lightly brush each meatball with olive oil to prevent sticking and promote a golden exterior. Arrange the meatballs directly over the heat. Grill, turning every couple of minutes, until all sides are seared and the internal temperature reaches a safe level, approximately 8 minutes in total.

Once cooked, transfer the meatballs to a serving platter and allow them to rest for 5 minutes to retain their juices. Serve hot alongside a bowl of warm marinara sauce for dipping.