1. To prepare dressing: Place orange zest, orange juice, vinegar, oil, oregano, mustard, salt and pepper in a jar. Cover and shake to combine.
2. To prepare salad: Slice both ends off orange. With a sharp knife, remove the peel and white pith; discard. Working over a large bowl, cut the segments from their surrounding membrane. Squeeze the juice into the bowl before discarding the membrane, if desired. If using tangelo or mandarin, just peel and section. Add lettuce, radishes, beans, scallion, feta and dressing; toss to coat. Refrigerate the extra dressing for up to 1 week.