In a large pot or dutch oven heat the olive oil on medium heat. Add in the diced onion, garlic, leeks and carrot and sauté for 5 minutes until soft.
Add the chicken broth and lemon juice to the pot and bring to a gentle simmer.
Add the kale to the soup along with the cooked meatballs.
Increase the heat so that the soup is just gently boiling and using a fork slowly pour in the egg in a thin stream. Don't pour too quickly otherwise you will get chunky clumps of egg in the soup. If you are going to freeze the soup I recommend skipping this step and waiting to add the egg right before eating.
Garnish the soup with parsley before serving.