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

Shape the mixture into golf ball-sized meatballs, about 1 to 1.5 inches in diameter. Place on a parchment-lined tray and refrigerate for 15-20 minutes.

In a large pot, pour in the chicken broth and olive oil. Heat over medium until simmering. Carefully add the meatballs in a single layer and simmer for about 30 minutes.

While meatballs simmer, whisk together the eggs and lemon juice in a bowl. Temper the eggs by gradually adding hot broth while whisking.

Return the tempered egg mixture to the pot with meatballs and stir gently, continuing to simmer on low heat.

Once the sauce has thickened slightly, remove from heat and serve warm, garnished with additional chopped dill or lemon wedges.