For the beets: Preheat the oven to 400 degrees F. Lay out a large sheet of foil on top of a roasting dish and spread the beets across evenly on the sheet. Drizzle with a little olive oil and season with salt and pepper. Top with another sheet of foil and crimp to seal the edges. Poke holes in the top to allow steam to escape. Place in the oven and roast until the beets are tender, 30 to 45 minutes. Remove from the oven. Allow to cool in the foil pouch before loosening the skins and discarding. Quarter the peeled beets and place in a large bowl.
For the cherry vinaigrette: Drain the cherries and roughly chop. Whisk together the vinegars (including the red wine vinegar from the cherries) and cherries while slowly drizzling in the olive oil so it lightly emulsifies. Season with salt and pepper. Set aside until ready to use.
For the salad: Toss the warm beets with the cherry vinaigrette. Add the kale, pepitas, goat cheese and mint, continuing to toss. Season with salt and pepper.