Cook pasta – Boil per package directions, drain, and cool slightly (rinse under cold water to speed this up).
Mix salad base – In a large bowl, combine pasta, onion, tomatoes, corn, and green onions. Toss.
Make dressing – In a separate bowl, whisk yogurt, garlic, oregano, chili flakes, salt, and lemon juice. Add water gradually until smooth and pourable.
Dress the salad – Pour dressing over pasta mixture; toss to coat evenly.
Finish – Add Parmesan and cilantro; toss once more.
Serve – Enjoy chilled or at room temperature.