Preheat the oven to 400°F/205°C.
Put the beets onto a baking tray and roast in the oven for approximately 45 minutes, until they are just tender to the touch. (You do not need to peel or trim them, or use any oil for this.)
While the beets are roasting, make the dressing. Add all ingredients to a small mason or jam jar, put the lid on and shake it vigorously for 10 seconds. Set aside.
When the beets are cooked, remove from the oven. Place them under gently running cold water as you peel the skin off them with your fingers. (You don't need to run them under cold water if they're cool enough for you to handle, but it does help making the peeling easier.)
Trim the ends of the beets, and using a mandoline or sharp knife, slice them into 3mm discs.
Arrange the slices on two plates in a scattered pattern, adding the artichoke hearts and arugula. Sprinkle with the toasted hazelnuts.
Gently drizzle the dressing over the top of the salad, and serve.