In a large bowl, combine eggs, milk, Parmesan cheese, breadcrumbs, oat flour, minced garlic, and grated onion. Mix thoroughly using a fork until well combined.
Add the ground meat to the mixture and gently combine, being careful not to overwork the meat to avoid tough meatballs. Use your hands or a spoon to mix until all ingredients are evenly distributed.
Once the mixture is combined, shape it into golf ball-sized meatballs, minimizing handling to keep them tender.
Heat olive oil in a large, deep non-stick pan over medium heat. Once the oil is hot, add the meatballs in batches, being careful not to overcrowd the pan. Cook for a few minutes on each side until browned and cooked through.
Once cooked, transfer the meatballs to a plate lined with paper towels to absorb any excess oil.