2 tablespoons extra-virgin olive oil, plus extra for drizzling
1 teaspoon fresh thyme leaves
salt and pepper
4 ounces (4 cups) baby arugula
2 ounces Pecorino Romano cheese, shaved with vegetable peeler
1/2 cup walnuts, toasted and chopped coarse
Adjust oven rack to middle position and heat oven to 400 degrees. Place 16 x 12 inch piece of aluminum foil on rimmed baking sheet. Arrange beets in center of foil and lift sides of foil to form bowl. Add water to beets and crimp foil tightly to seal. Roast until beets can be pierced easily with fork, 1 & 1/4 to 1 & 1/2 hours.
Once beets are cool enough to handle, rub off skins with paper towels. Halve each beet vertically, then cut into 1/2 inch-thick wedges.
Whisk vinegar, oil, thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper together in a large bowl. Add beets and toss to combine. Cover and refrigerate for at least 30 minutes or up to 24 hours.
Cut away peel and pith from oranges. Holding fruit over bowl, use paring knife to slice between membranes to release segments; set aside. Arrange arugula on serving platter. Spoon beets over arugula and drizzle with remaining marinade. Arrange orange segments over salad and top with Pecorino and walnuts. Season with salt and pepper to taste. Drizzle with extra oil and serve!