1.Boil, steam or microwave potato until just tender; drain. Cover and refrigerate 30 minutes.
2.Meanwhile, combine juice, oil, sour cream and garlic in a screw-top jar; shake well. Combine beans, onion, parsley, chilli, capsicum, avocado and coriander in large bowl.
3.Add potato to bean mixture, pour dressing over salad and toss gently to combine. Serve with warmed tortillas.