The salad holds well, so you can make it up to a day ahead.
To prepare salad, cook beans in boiling water for 12 minutes. Drain; rinse with cold water. Drain. Combine beans, corn, and next 5 ingredients (corn through oregano).
To prepare dressing, combine lemon juice and remaining ingredients, stirring with a whisk. Drizzle over salad, and toss to coat.