Bring large pot of lightly salted water to boiling for the pasta. Add pasta; cook for about 11 minutes or until firm but tender. Drain the pasta; rinse under cold running water to stop the cooking; drain well.
Meanwhile, whisk together the vinegar, orange juice, olive oil, oregano, salt and pepper in large bowl. Add the kidney beans, orange pieces, celery, sweet yellow pepper, green onion, radishes and half of the crumbled feta.
Stuff the shells with the vegetable mixture, dividing equally. Spoon any leftover dressing from bottom of bowl over the top of the stuffed shells. Arrange the shells in a serving platter. Sprinkle evenly with the remaining crumbled feta. Garnish with fresh oregano leaves, if you wish. Makes 6 servings.