Rinse the leek thoroughly under running water to remove all sand, then slice it into rings. Rinse the two zucchini and cut them into rough chunks. Rinse the 250 grams of canned white beans thoroughly in a colander and let them drain. Have the liter of sugar-free and yeast-free vegetable broth ready to use.
Heat the tablespoon of olive oil in a large soup pot over medium heat. Add the sliced leek and sweat it for five minutes until the rings are soft. Then add the zucchini chunks to the pot and pour in the vegetable broth. Bring everything to a boil, reduce the heat, and let the soup simmer gently for fifteen minutes until the zucchini is cooked through.
Remove the pot from the heat. Blend the cooked vegetables in the broth with an immersion blender until you have a smooth and creamy soup. Return the pot to the stove and add the drained white beans to the soup. Stir everything well and reheat for two more minutes over low heat, so the beans also come up to temperature.
Ladle the warm zucchini soup into deep bowls or cups. Garnish the dish by distributing the two tablespoons of pumpkin seeds evenly over the portions and serve immediately.