In a large pot or Dutch oven over medium heat, warm olive oil, then add chopped leeks, carrots and celery. Stirring occasionally, cook about 5 minutes, or until leeks are softened and wilted.
Stir in garlic and cook for 1 minute. Add herbs and red pepper flakes and cook until fragrant, about another minute.
Add the vegetable broth and beans, then bring the soup to a slight boil. Add kale to the pot, and turn down the heat to low. Cook until kale softens and wilts. Add the lemon zest and juice, then add salt and pepper to taste. If soup seems too thick, add extra water or broth as needed.
Garnish each serving with parsley if desired.
Can be kept in the refrigerator for up to a week before the party.