Preheat the oven to 400°F if baking, or heat a skillet with oil if pan-frying
In a large bowl, combine ground beef, breadcrumbs, egg, grated onion or minced onion, minced garlic, salt, black pepper, and parsley
Add a little milk or water if the mixture seems too dry
Mix gently until just combined
Shape the mixture into evenly sized meatballs
Place the meatballs on a baking sheet or plate
Bake for 15 to 20 minutes, or cook in a skillet until browned on all sides and cooked through
Check that the internal temperature reaches 160°F
Serve with sauce, pasta, rice, or as desired