In a large microwave-safe bowl, toss the beans with the dried mint (if using) and ½ teaspoon salt. Cover and microwave on high until hot, 3 to 3½ minutes, stirring once halfway through. Add the onion, vinegar and ¾ teaspoon pepper to the hot beans, toss, then let stand for about 30 minutes, stirring once or twice.
Stir in the tomatoes, olives, chilies and lemon zest. Taste and season with salt and pepper, then transfer to a serving dish. Serve drizzled with oil.
