How to Make It
Preheat the oven to 375°. Arrange the beets in a baking dish and fill with 1/4 inch of water. Cover with foil and bake for 45 minutes, or until tender. Let cool, then peel the beets and cut them into 1/2-inch-thick wedges.
In a very large pot of boiling salted water, cook the beans over high heat until crisp-tender, about 5 minutes. Drain and refresh under cold water. Drain well and pat dry.
In a small bowl, whisk the olive oil with the vinegar until blended. In a large bowl, toss the beans with 1/2 cup of the vinaigrette and transfer to a platter. In the same large bowl, gently toss the beets and chives with the remaining 1/4 cup of vinaigrette and spoon over the beans. Season with salt, sprinkle the feta on top and serve.