In a large bowl, combine the ground beef, grated onion, arborio rice, parsley, dill, egg, oregano, salt, and black pepper. Mix until well incorporated.

Form the meat mixture into golf ball-sized meatballs and chill on a parchment-lined baking sheet for 15-20 minutes.

In a large pot, combine chicken broth and olive oil over medium heat, bringing to a gentle simmer.

Carefully add the chilled meatballs to the simmering broth, cover, and cook undisturbed for 30 minutes.

In a medium bowl, whisk together eggs and lemon juice, then temper with hot broth slowly while whisking.

Return the tempered mixture to the pot, stirring over very low heat until the sauce thickens slightly, being careful not to boil.