NOTE: If unable to find Tamarind Concentrate, (Available in Indian or Middle Eastern stores), use plum butter (available in Health Food stores), plus 2 Tb of Fresh Lemon Juice. These are a substitute for the local Georgian Sour Plum paste that is unavailable here.
Combine the beans with the onion, carrot, and celery in a soup pot. Add enough water to cover the beans by 3-inches and bring to a boil. Add the salt, then reduce the heat to low, cover and cook the beans until tender but not mushy, about 55 minutes or more, depending on the beans. Meanwhile combine the prunes and the balsamic vinegar in a saucepan and simmer for about 15 minutes. Remove the prunes with a slotted spoon and reserve the vinegar. Finely chop the prunes. Add the tamarind concentrate to the vinegar and let stand until dissolved, about 10 minutes. Stir well and set aside. Drain the beans and discard the onion, carrot, and celery. Place the beans in a serving dish and allow to cool. In a small bowl, whisk together the diluted tamarind mixture, the chili paste, and the olive oil, blending well. Add the chopped prunes, coriander seeds, and fenugreek, again blending well. Toss the beans with the tamarind mixture. Taste and correct the seasoning and stir in the 1/4 cup of cilantro leaves. Refrigerate, covered, for at least 2 hours before serving. Serve, garnished with the additional cilantro and the onion rings.