Arrange the arugula, red onions, and olives in a serving bowl or platter.
Briefly mix the oil and vinegar.
Drizzle them over the vegetables.
Sprinkle the salad with kosher salt and black pepper.
Top the salad with shaved parmesan cheese.
Serve the pretty salad, and only then toss it at the table and divide it into individual plates.
Video
Notes
You can add protein such as chicken or shrimp to the salad and turn it into a main dish salad.
You can assemble the salad a few hours in advance, loosely cover it with paper towels, and refrigerate it. Don't add the dressing until the last minute, or the greens will become soggy.
This is such a pretty salad. I like to bring it to the table nicely arranged on a platter, and only then do I mix it and divide it between the diners.
As with all salad greens, once the salad is ready and you've added the dressing, I don't recommend keeping its leftovers. You should only make as much as you can finish right away.