In a large bowl, combine the ground beef, breadcrumbs, Parmesan cheese, diced onion, minced garlic, egg, salt, and pepper. Mix well.
Use your hands to shape the mixture into small meatballs, about 1-1.5 inches in diameter.
Heat a large skillet over medium-high heat and add the olive oil. Once the oil is hot, add the meatballs to the skillet.
Cook the meatballs for about 8-10 minutes, or until they are browned on all sides and cooked through.
Serve the meatballs as an appetizer with a dipping sauce of your choice or add them to your favorite pasta sauce and serve over spaghetti.