Roast the beets - Preheat the oven or your air fryer to 400℉. Trim the beet greens and reserve them for another purpose. Rub the beets all over with a bit of olive oil, wrap them in aluminum foil, and roast for 50 minutes to an hour, or until the beets are softened all the way through and can be easily pierced with a fork. Remove the beets from the oven and when they're cool enough to handle, gently rub off the skins, then chop the beets into 1-inch cubes. I recommend wearing gloves, or you'll have pink palms the rest of the day!
Mise en place - While the beets are roasting, cut the onion pole to pole. Cut each of the halves across, then slice it vertically. Soak the onion slices in 1 T of white vinegar and sprinkle with ½ t of salt. Gently massage the salt into the onion, and let it macerate until you're ready to compose the salads. Wash and dry the lettuce.
Compose the salad - Spoon a tablespoon of vinaigrette into the bottom of each salad bowl, then tear the lettuce leaves into bite-sized pieces and distribute them among the bowls. Carefully distribute the beets on top of the lettuce, so that you don't stain the lettuce. Scatter ¼ of the onion slices and 1 T of crumbled goat cheese on top of the beets. Then, finally, distribute the pistachios evenly over each salad.