To cook beets, cut off all but 1 inch of stems and roots; wash. Do not peel. Cook, covered, in boiling salted water for 40 to 50 minutes or until just tender. Drain; cool slightly. Slip skins off beets. Cut beets into 1/4-inch-thick slices. (You should have 2 cups).
Meanwhile, for dressing in a screw-top jar combine walnut oil or salad oil, orange peel, orange juice, and vinegar. Cover and shake well.
In a medium mixing bowl gently toss the beet slices with the dressing. Cover and chill for 2 to 24 hours.
To serve, let mixture come to room temperature. Gently stir nuts into beets. Sprinkle with feta cheese and pepper. Serve with a slotted spoon. Makes 4 servings.