In a large bowl, combine the olive oil, lemon juice, onion, and salt and pepper.
Add the shrimp, orzo, avocado, tomatoes, corn, and jalapeño, and toss to coat with the dressing.
Transfer to a serving bowl. Garnish with the cilantro, if using.
Notes
You can cook the orzo, shrimp, and corn a day or two ahead of time.
You can use pre-cooked shrimp if you want to deal with even less prep!
The dressing can be made up to 3 days ahead of time.
The best way to prep this dish ahead of time is to assemble the whole salad, minus the tomatoes and avocados, up to one day ahead of time. Add the tomatoes and avocados just before serving, and bring the salad to cool at room temperature before serving for the best flavor.