Roast Beets: Preheat oven to 400 degrees F (204 C). Peel and dice beets, then spread onto a parchment-lined rimmed baking sheet. Drizzle with oil, tossing to evenly coat, then roast for 30 minutes, or until fork-tender.
Cook Couscous: Meanwhile, bring water to a boil in a medium pot and add couscous. Cover and cook for about 10 minutes, or until couscous is “al dente” and water is absorbed.
Toss Together: When beets are hot out of the oven, mix them in with the cooked couscous, along with any beet juice in the pan, lemon juice, salt, and pepper, stirring to spread the bright pink juices of the beets onto the couscous. Toss with feta cheese and serve (warm or chilled)