Cook the orzo according to package directions.
While the orzo is cooking, prepare the cucumbers, tomatoes and red onion and add to a large mixing bowl. Add the olives.
Combine all the ingredients for the dressing and whisk to combine.
Once cooked, drain the orzo and add to the mixing bowl with the vegetables. Pour the dressing on and mix well. Add the crumbled feta and arugula and mix again. Refrigerate for an hour to allow the flavours to combine and serve. This salad will keep in the fridge for only one day because the arugula will get to wilted.