Heat olive oil in a large pot over medium heat. Add diced onion and sauté for 5 minutes until softened. Add minced garlic and cook for 1-2 minutes until fragrant, stirring frequently to prevent burning.
Pour in the vegetable broth and add the white beans, rosemary, oregano, salt, black pepper, and red pepper flakes. Bring to a boil, then reduce heat and simmer for 10 minutes.
Use the back of a wooden spoon to gently mash about one-third of the beans against the side of the pot to help thicken the soup naturally.
Add the chopped kale to the pot and stir well. Simmer for 8-10 minutes until the kale is tender and wilted.
Remove from heat and stir in fresh lemon juice. Taste and adjust seasonings as needed before serving.