In a large bowl, combine the bread crumbs, parmesan, grated onion, egg, garlic, Worcestershire sauce, salt, and pepper and mix well.
Add the ground beef and use your hands or a strong spoon to mix everything together until evenly dispersed.
Roll the meat mixture into 1 to 1 ½-inch balls and place on a baking sheet. You should get about 20 meatballs from the mixture. At this point, you can cover and refrigerate the meatballs for up to 2 hours if desired.
Preheat the Blackstone to medium-high. Slick generously with oil.
Place the meatballs on the griddle, leaving a couple of inches between each meatball. Cook, turning occasionally, until the meatballs are cooked through and the internal temperature reaches 160°F (71°C), about 12 minutes.
Notes
Size matters--Don't make your meatballs any larger than 1 ½-inches (4-cm) in diameter. Meatballs that are too large will burn on the outside before fully cooking in the center.
Rolling the meatballs--Roll your meatballs firmly enough that they stick together but don't pack them tightly, as this may cause them to become tough.
Avoid sticking--Slick the griddle well with oil before adding the meatballs to avoid sticking. Slick the griddle well with oil before adding the meatballs to avoid sticking. I recommend using a thin metal spatula to turn them. This will help to loosen them from the griddle and also prevent them from falling apart.