Sauté the onion, leek and celery in water in a large soup pot until translucent, about 5 mins. Add in the garlic and cook for another new minutes, until it is fragrant.
Add in the remaining ingredients (except for the lemon juice and cilantro) and bring it to a boil. Once boiling, lower to a simmer and cover for 30-40 mins or until the squash is fork tender.
Cool for 10 mins, then place into a high speed blender with the lemon juice (in 3 batches) and run until smooth. Add in the cilantro and pulse until it is mixed through.