1. Using a juicer, juice the lovage (or celery leaves). Measure out 4 teaspoons of the juice.
2. Combine the miso, rice wine vinegar, and olive oil in a mortar and stir gently with a spoon to loosen the miso; you may need to add a little more vinegar and oil. Add the walnuts and pound with the pestle until the mixture has the consistency of chunky peanut butter, with some larger pieces of nuts or even some whole nuts still visible.
3. Put the zucchini in a large bowl and toss together with the chardonnay vinegar, lemon zest, lemon juice, and a pinch of kosher salt; do not let this sit for more than a few minutes, as you want to preserve the texture of the zucchini. Spoon and casually smear the walnut mixture in scattered clusters on your serving plate, leaving a border. Spoon lovage juice into the gaps between the dollops of the nut mixture.
4. Arrange the zucchini on top, as neatly or sloppily as you like, and sprinkle with a pinch or two of gray salt and a dusting of pimentón dulce.