Preheat oven to 400 degrees F. Wash beets well. While still wet, wrap them individually in foil and place on a cookie sheet or roasting pan. Bake beets, undisturbed, for 60 to 90 minutes, until a thin-bladed knife pierces each with little resistance. (They may cook at different rates; remove each one when it is done.)
Meanwhile, put oil in a skillet over medium-low heat. When it is warm, add garlic and cook until fragrant and beginning to soften, about 6 minutes. Add walnuts and continue to cook until they begin to color, about another 4 minutes. Let mixture cool slightly and then put it in a small food processor; process until you have a relatively smooth paste. Add orange juice to taste and sprinkle with salt and lots of pepper.
After beets have cooled, peel off skins. Slice beets into wedges or cubes and toss with dressing. Taste and adjust seasoning, garnish with parsley and serve.