Drain the beans, rinse, and cover with 4 to 6 cups fresh water. Add the onion and all but 1 of the cloves, bring to a boil. Reduce heat and simmer for about 1 hour, until the beans are very soft. Drain the beans, onions, and garlic, and reserves the remaining bean liquid. Place the bean mixture in the container of a food processor and puree, adding enough cooking liquid to make a soft puree. Season with slt and pepper. Set aside. Chop the sun-dried tomatoes and soak them for 15 to 30 minutes in just enough bean cooking liquid to soften and release their flavor. Fold the tomatoes into the beans. Fold in the yogurt. In a large saute' pan over high heat, wilt the greens in the vinegar. Drain well and season with salt, pepper, hot pepper flakes, and additional vinegar, if desired. To assemble the crostini, grill or toast the whole grain bread. While warm, rub it with the remaining garlic clove, cut in half. Spread the bread slices with white bean puree and top each with chopped greens. Serving size = 1 slice 152 calories 1.5 grams fat 1.1 milligrams cholesterol 247.4 milligrams sodium without added salt