In a large mixing bowl, combine the ground beef, grated onion, uncooked arborio rice, freshly chopped parsley, dill, one egg, oregano, salt, and black pepper. Gently mix all the ingredients together using your hands until just combined.

Dampen your hands with water and shape the mixture into golf ball-sized meatballs. Chill in the refrigerator for about 15-20 minutes.

In a pot, pour in the chicken broth and a splash of olive oil, then bring to a gentle simmer. Add the chilled meatballs and cover. Simmer on low for about 30 minutes.

For the Avgolemono sauce, whisk together the eggs and the lemon juice. Gradually temper the eggs with hot broth while whisking.

Slowly pour the tempered sauce back into the pot with the meatballs while stirring gently. Heat on very low until the sauce thickens slightly.

Ladle the meatballs with sauce into bowls and garnish with dill or lemon wedges. Serve warm.