Salad of White Beans & Greens (Fasolia me Horta)

Sort beans, discarding any debris. Rinse and place in a large bowl. Cover with cold water and let soak for at least 8 hours or overnight. (Alternatively, place beans in a large pot, cover with water and bring to a boil. Boil for 2 minutes. Remove from the heat and let stand for 1 hour.) Drain beans and place in a large saucepan. Cover with fresh water and bring to a boil. Reduce heat to low and simmer, covered, until tender, about 45 minutes, adding water if necessary. Drain and refresh with cold water. Set aside. With the water still clinging to the leaves, place greens in a large pot. Cover and cook over medium-high heat, stirring occasionally, until just wilted, 2 to 3 minutes. Drain, pressing out as much liquid as possible. Roughly chop. Combine onions, vinegar and sugar in a small, nonreactive saucepan. Cover and bring to a boil. Immediately, remove from the heat and let stand, covered, for 5 minutes. Combine the reserved beans, greens, onion mixture and remaining ingredients in a large serving bowl. Taste and adjust seasonings.