Roast the beets. Preheat the oven to 350. Place each beet on a piece of foil. Add a drizzle of oil and rub to coat the beet in it. Repeat for all beets. Roast for 40 minutes to an hour, until the beets are fork-tender. The timing will depend on your oven and how thick the beets are.
While the beets are roasting, make the dressing. Add the lemon juice to a liquid measuring cup. Slowly drizzle in the olive oil, whisking vigorously to ensure the dressing emulsifies.
Once the beets are done, remove them from the oven and unwrap the foil. Let them cool for 10-15 minutes, then peel them. Using a spoon or the dull side of a paring knife, scrape the peels off. They should come off easily. You can do this in the sink under running water to avoid staining anything. Cut the beets into 1” chunks.
Assemble the salad. Place arugula in the serving dish you’ll be using, then add the dressing and toss. Next, scatter the onions, citrus and apple slices on top. Then, arrange the beets on top. Heads up — the beets will color anything they touch! This won’t affect the taste, but the apples will pick up color from the beets. Next, scatter the goat cheese crumbles over the salad, then the pistachios. Enjoy!