Drain the soaked giant beans and place in a medium saucepan with fresh water. Bring to a boil and simmer over medium heat for about 1 to 1½ hours, or until tender but al dente. Drain and cool.
Coarsely chop the arugula and add it to a large mixing bowl.
Remove the cucumber ends and cut the cucumber in half lengthwise and then into ½-inch (1¼-cm) half-moon-shaped pieces.
Cut the bell pepper in half, into ¼-inch strips, and then in large dice.
5, When the beans are cool, place them in a large salad or mixing bowl. Onions and cucumbers go next. The two types of tomatoes and scallions are added to the bowl.
Place half of the feta in the salad bowl with the beans and other vegetables. Add the pickled peppers around the circumference of the bowl. Add the olives and capers, as well.
Make the vinaigrette by adding lemon juice, mustard, and oregano in a medium bowl and whisk olive oil until the dressing emulsifies.
Top the salad with lemon zest and finish with a few tablespoons of dressing. Drizzle the rest of the vinaigrette before serving.