In a large mixing bowl, combine ground beef, finely grated onion, uncooked Arborio rice, chopped parsley, dill, egg, dried oregano, salt, and black pepper. Mix gently until all ingredients are just combined.

Using your hands, form the meat mixture into golf ball-sized meatballs, placing them on a parchment-lined tray. Cover with plastic wrap and refrigerate for 15–20 minutes.

In a wide, heavy-bottomed pot over medium heat, pour in chicken broth and add olive oil. Bring this mixture to a gentle simmer for about 5 minutes.

Carefully add the chilled meatballs to the simmering broth, cover the pot and reduce the heat to low. Let the meatballs simmer for 30 minutes.

In a separate bowl, whisk together the eggs and lemon juice until the mixture is smooth. Gradually add hot broth from the pot while whisking continuously.

Return the tempered egg-lemon mixture to the pot with the meatballs, stirring gently. Heat on very low for about 5 minutes until the sauce thickens slightly.

Serve the meatballs warm in shallow bowls, drizzling them with the lemon sauce and garnish with additional chopped dill or lemon wedges as desired.