Position a rack in the center of the oven and heat the oven to 425 degrees. Line a heavy-duty rimmed baking sheet with foil. Place the peppers and corn on the baking sheet. Drizzle the oil over the peppers and corn and rub it around to coat the pepper skins and corn kernels evenly. Sprinkle the corn with salt and pepper. Roast in the oven until the peppers are soft, slightly shriveled and browned, and the corn kernels are lightly browned in a few spots, about 20 minutes. Rotate the corn occasionally as it roasts.When the vegetables are done, let them rest until cool enough to handle. Scrape away the pepper skin and dice the flesh into 1/2 inch pieces. Cut the corn kernels from the cob. You should have about 1 1/2 cups kernels. Core, seed and dice the tomatoes into 1/4 inch pieces. Peel and dice the jicama into 1/4 inch pieces. Peel, pit and dice the avocados into 1/4 inch pieces.Artfully arrange the corn, tomatoes, peppers, jicama, avocado and black beans in strips or piles on a small platter or wide, shallow serving dish. Sprinkle with the chopped cilantro. Serve with Citrus Cumin Dressing in a pitcher. Encourage guests to spoon elements of the salad onto their plates and drizzle on some of the vinaigrette. Or drizzle the vinaigrette over the salad platter just before serving.