1. Cook orzo according to package directions, omitting salt and fat. Drain and rinse; drain well. Place orzo, corn, and next 3 ingredients (through beans) in a large bowl; toss.
2. Combine buttermilk, 2 tablespoons cilantro, and next 8 ingredients (through garlic) in a small bowl, stirring well with a whisk. Drizzle over orzo mixture; toss. Top with avocado; garnish with remaining cilantro and parsley.