In a large bowl, combine the meat, egg, breadcrumbs, cheese, onion, garlic, salt, pepper, and parsley, if using.
Use a medium cookie scoop or spoon to scoop the meat mixture. Form into 1 ½-inch balls and place on the baking sheet.
Heat the olive oil in a large cast-iron skillet over medium heat. Add the meatballs and cook for around 5-7 minutes—or until the meatballs are cooked and only slightly pink on the inside.
Simmer meatballs with marinara sauce, if desired, for 10 minutes.
Serve meatballs on their own or serve over spaghetti noodles. Top with Parmesan cheese and fresh herbs, if desired.
