Wash your beets thoroughly, top and tail them, and the place them on a large sheet of aluminium foil. Drizzle with olive oil and season with salt and pepper. Wrap tightly in the foil, place on a tray, and bake in a 400 degree oven for about 60-90 minutes. You want them to be easily pierced with a knife.
Remove from the oven and set aside to cool. You can do this the day before and leave them in the fridge overnight.
Remove beets from the foil and using a paring knife, peel the skins off.
Cut the beets into small squares, about 1/2 cm wide. Add them to a large bowl.
Add to the bowl with the beets the vinegar, capers, mustard and vegan mayo or toum. Season well with salt and pepper, and taste to determine if they need more seasoning. Set aside.
Toss your arugula with a little olive oil, salt and pepper. Place it on a pretty plate.
Mound the beet tartare on top of the arugula, and garnish with vegan feta (if using) and parsley.