In a Dutch oven, heat olive oil or butter to medium heat. Add the onion and jalapeno and sauté 5-6 minutes or until slightly soft. Add the zucchini and sauté another 5-6 minutes or until soft. Stir in the garlic, salt, black pepper and celery salt 30-60 seconds or until the garlic is fragrant.
Add the stock and bring to a simmer for 8-10 minutes or until the zucchini is very soft. Use an immersion blender to puree the soup until smooth. (Alternatively, transfer the mixture to a blender and puree until smooth, then place back in the pot.)
Stir the lemon zest and juice and half and half or cream into the soup. Taste and adjust seasoning, if necessary.
