1. Clean leeks: Cut off the root and most of the green part of the leeks, so only the white and light green parts remain. Split leeks down the middle and wash well under running water. Transfer to a clean cutting board and slice thinly. Set aside.
2. Heat olive oil in a large, heavy-bottomed pot. Add the parsnip and sauté for five minutes. Add the zucchini and cook two more minutes. Add the leeks and season with salt and pepper. Cook until leeks are softened but still bright green, about 10 minutes.
3. Add chicken stock and water and bring to a boil. Reduce to a simmer and allow to cook for 20–30 minutes.
4. Cool and blend.