Heat the olive oil in a large pot over medium heat. Add the chopped leeks, carrots, celery, and garlic. Season with a pinch of salt and pepper. Saute the vegetables for 3 - 5 minutes, until tender.
Add the drained and rinsed cooked chickpeas to the pot. Stir all the ingredients together. Cover the pot, stirring frequently, until the chickpeas are tender, about 8 - 10 minutes.
Add the lemon juice, vegetable stock, herbs, and ground nutmeg. Bring the soup to a low boil and simmer for 15 minutes.
Remove the bay leaf and carefully puree the soup (using an immersion blender or transfer half of the soup at a time to a blender) until smooth and creamy.
If you are using a blender, be very careful with the amount of hot liquid you add. Too much will create pressure from inside and it will blow the lid off. I like to put a cloth towel over the lid as a precaution.
Season with salt and pepper to taste. Ladle the soup into bowls, drizzle with olive oil, and enjoy!