Carefully stir together the pasta, beans, scallions, olives, peppers, fennel, celery, ½ teaspoon dried oregano, and ¾ of the feta cheese. Add a small pinch of kosher salt (the feta is salty; don’t salt too much), a generous pinch each of freshly ground black pepper, and crushed red pepper. Pour half the vinaigrette over the salad; stir gently. Taste and adjust seasonings. (If making ahead, add only a drizzle of vinaigrette, stir and store covered overnight. Dress and garnish salad just before serving.)