This salad is easy, delicious, and colorful, perfect for taking advantage of fresh seasonal corn and tomatoes. It combines black beans with fresh lime juice, olive oil, corn kernels, plum tomatoes, scallions, fresh flat-leaf parsley, and a touch of cayenne for a slight spice. The mixture is marinated for 15 minutes to allow the flavors to intensify and is then served over Boston lettuce leaves. You can use regular tomatoes if you don't have plum tomatoes, and flat-leaf parsley is recommended for its better flavor. You can also substitute the lettuce with radicchio or another variety, or even omit it. The salad tastes even better the next day and is best served at room temperature to maximize its flavor.