How to Make It
Preheat the oven to 450°. Wrap the beets in foil and roast for about 1 hour, until tender. When cool enough to handle, slip off the skins and cut the beets into wedges. Tear the beet greens into bite-size pieces; you should have about 2 cups.
Meanwhile, in a medium saucepan of boiling water, cook the lentils until tender, about 20 minutes. Drain and cool under running water; drain well.
In a large bowl, whisk the olive oil with the mustard, lemon juice and scallions. Add the lentils, beets and beet greens and season with salt and pepper; toss and serve.