In a large mixing bowl, combine ground beef, finely grated onion, rinsed arborio rice, fresh parsley, dill, egg, dried oregano, salt, and black pepper. Mix until just combined.

Roll the mixture into golf ball-sized meatballs, about 1.5 inches in diameter. Refrigerate for 15-20 minutes.

In a pot, bring chicken broth and olive oil to a gently simmer. Add chilled meatballs in a single layer, cover, and simmer for 30 minutes.

Whisk together eggs and lemon juice in a bowl. Gradually add hot chicken broth to temper the eggs while whisking.

Remove pot from heat and slowly stir in the egg-lemon mixture, stirring over low heat until warmed through without boiling.

Ladle the warm meatballs and sauce into serving bowls, garnishing with additional chopped dill or lemon wedges.