Cook the beets with skin in a pressure cooker for 15 minutes (after getting the pressure).
Let it cool (it can help putting it in the fridge), and slice the beets very thin, in a mandolin or regular vegetable slicer.
Arrange the slices on a plate from the center to the edges, like a snail.
Add the arugula and flowers.
For the sauce, just mix the other ingredients well.
Tips:
You can bake the beets wrapped in aluminum foil for 20 to 30 min, using the oven on for another preparation.
You can leave the boiled or roasted beets in the fridge for up to 3 days, to assemble the salad later.