In a large bowl, combine the ground chicken, Parmesan, breadcrumbs, egg, salt, pepper, oregano, parsley, and red pepper flakes. Mix until just combined, then form into 1-inch meatballs.
Heat the olive oil in a skillet over medium heat. Sear the meatballs on all sides until golden brown, about 4–6 minutes. Transfer to a paper towel-lined plate and set aside.
In a large soup pot, heat 1 tablespoon of olive oil over medium heat. Add the onion, garlic, and red pepper flakes and sauté for 3–5 minutes until fragrant and translucent.
Pour in the stock, salt, and pepper. Bring to a simmer. Add the kale and cook for 3 minutes until wilted.
Add the meatballs and cannellini beans to the pot and simmer for 8 minutes until the meatballs are cooked through.
In a small bowl, whisk together the egg and Parmesan. Slowly drizzle the mixture into the simmering soup while stirring gently to create silky strands.
Stir in the lemon juice, taste, and adjust seasoning as needed. Serve hot with extra Parmesan on top.