Cook orzo according to package directions, omitting salt and fat. Drain and rinse.
Allow corn to thaw while prepping remaining veggies. Quarter cherry tomatoes, slice green onions, and rinse and drain black beans; toss all into a large bowl with the orzo.
Combine buttermilk, chopped cilantro, lime juice, sour cream, mayo, chili powder, salt, pepper, cayenne (optional), and crushed garlic in a small bowl, whisking to combine.
Drizzle over orzo mixture and toss to evenly coat. Dice avocado and chop parsley.
Top orzo with avocado and parsley, and serve with raspberries on the side.