Bring a large saucepan 3/4 full of salted water to a boil over high heat.
Add the shrimp and simmer until pink, about 5 minutes. Drain the shrimp and rinse quickly under cold water.
Meanwhile, in a bowl, combine the garlic, lemon juice and red pepper flakes. Add the hot shrimp to the garlic mixture and marinate for 10 minutes along with orzo.
In a large bowl, toss together the shrimp/orzo mixture with the marinade, scallions, red onion, capers, celery, fresh corn and tomatoes, and set aside.
To make the dressing, in a small bowl, whisk together the oregano, olive oil, salt, pepper, lemon juice, and vinegar. Pour over the shrimp, orzo, and vegetables, add the parsley, and toss to incorporate. Cover and refrigerate until ready to eat. Serve chilled.