A great soup. Very delicious with two little adjustments. The recipe is from Washington Post.
1 tablespoon extra-virgin olive oil
1 cup chopped onion
2 medium cloves garlic, minced
2 pounds zucchini (4 medium), trimmed, halved lengthwise and cut crosswise into 1/2-inch half- moon slices
3/4 teaspoon salt, or more as needed
2 cups low-sodium chicken broth (see headnote; may substitute vegetable broth)
Flesh of 1 ripe avocado
1/3 cup packed fresh basil leaves (I used half a cup).
1 teaspoon finely grated lemon zest and 1 tablespoon juice (from 1 lemon), or more as needed (I used two lemons)
Pinch ground white pepper
Heat the oil in a large pot over medium heat. Once the oil shimmers, add the onion and cook for 3 minutes, until it is softened. Stir in the garlic and cook for 30 seconds, then stir in the zucchini and the salt.
Add the broth and increase the heat to medium-high; once the liquid begins to boil, reduce the heat to medium-low, cover and cook for about 8 minutes, or until the zucchini has softened. Let cool completely.
Puree half of the zucchini mixture in a blender, then transfer the puree to a large bowl or storage container. Add the remaining half of the zucchini mixture to the blender with the avocado and the basil; puree until smooth, then add it to the first batch of pureed mixture.
Stir in the lemon juice, zest and the pepper. Taste, and add more salt and/or lemon juice. Cover and refrigerate for at least 2 hours, and up to 1 day, before serving.