Place broth, zucchini and tarragon (or dill) in a medium saucepan; bring to a boil over high heat. Reduce to a simmer and cook, uncovered, until the zucchini is tender, 7 to 10 minutes. Puree in a blender (see Tip), in batches if necessary, until smooth. Return the soup to the pan and heat over medium-high, slowly stirring in cheese until it is incorporated. Remove from heat and season with salt and pepper. Serve hot or chilled.