Preheat oven to 400 degrees F. Peel and dice beets, then spread onto a parchment-lined baking sheet. Drizzle with oil, tossing to evenly coat, then roast for 30 minutes, or until fork-tender.
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.
When beets are hot out of the oven, mix them in with the cooked couscous, cubed feta, along with the lemon juice, salt, and pepper, stirring to spread the bright pink juices of the beets onto the couscous.