In a large bowl, combine 2 cups water with lime juice. Carefully peel sunchokes and slice thinly. Immerse them in lime juice/water mixture, and set aside. Peel and halve cucumber. Remove seeds and slice thinly on the bias. Slice radishes thinly. Peel carrots and slice thinly. Remove sunchokes from water and pat dry.
In a large bowl, combine sliced vegetables, bread cubes, beans, and chopped mint. On a large platter or on each of six serving plates, arrange a layer of salad greens. Add Harissa Dressing to vegetables and toss well. Spoon over greens and sprinkle with feta.
In a blender or food processor, puree lemon, harissa, shallots, and vinegar. With the motor running, slowly add walnut oil, then grapeseed oil. Season to taste with salt.