Heat oven to 400 F.

Peel beets, cut into 1/2-inch wedges and toss with olive oil and salt and pepper, keeping red and yellow beets separate. Place beets on foil- or parchment-lined baking sheet. Roast until a sharp knife pierces beets easily, about 35-40 minutes. Let cool.

While beets are roasting, whisk together garlic, vinegar, tamarind, walnut oil and salt and pepper to taste. Toss beets with some of the dressing. Divide arugula among 4 serving plates and top with beets. Sprinkle with grapes, drizzle with more dressing, sprinkle with walnuts and serve.