It's the acid tang of the citrus next to the creaminess of the avocado that makes this combination such a classic, but there's no need to be limited to grapefruit. Give other citrus a try as well.
1 very small red onion, sliced into thin rounds, about 1/3 cup
2 tablespoons white wine vinegar
1 bunch watercress
1 small pomegranate
3 red grapefruits or a mixture of citrus fruits
1 large avocado, such as a Pinkerton or Reed
grated zest and juice of 1 tangelo or Satsuma mandarin
sea salt and freshly ground pepper
2 tablespoons extra virgin olive oil
1/4 cup roasted pistachio nuts, coarsely chopped
1. Toss the onion rings with the vinegar and set them aside in the refrigerator. Sort through the watercress and discard the large, heavy stems. Rinse under cool running water, spin dry, then wrap in a towel and refrigerate until ready to use.
2. Cut the pomegranate into quarters, then break out about 1/2 cup of the seeds. Working in the sink, gently squeeze a tablespoon or so of juice from the remaining pomegranate and set it aside. Peel and section the grapefruits. Neatly peel and thinly slice the kiwi. Peel and cut the avocados into neat chunks.
3. To make the dressing, combine the zest, 1/4 cup tangelo juice plus 1 tablespoon pomegranate juice, and 1/4 teaspoon salt, then whisk in the oil.
4. Loosely arrange the watercress on a plate with the grapefruit sections (minus their juice). Add the kiwi, avocado, and onions, which will be pickled by now, then pour the dressing over all. Season with pepper and garnish with the pistachio nuts.