Summer's heirloom tomatoes are combined with white and sweet potatoes and fresh greens in a salad tossed with a spicy southwestern dressing. Creamy goat-cheese slices are served on top.
Place the potatoes in a large saucepan of cold salted water. Bring to a boil, reduce to simmer, and cook until the potatoes are just tender, 20 to 25 minutes. If sweet potatoes are done before, remove with slotted spoon to colander. Drain the potatoes in colander, and rinse with cold water. When cool enough to handle, peel, and cut into 1-inch chunks.
Transfer potatoes to a medium bowl; add reserved poblano pieces and half of dressing. Stir to combine well. Place lettuces in large bowl. Drizzle with olive oil, and sprinkle with salt and pepper. Cut tomatoes into halves, slices, or wedges, and toss well with greens.
If plating salads individually, arrange greens on six plates, and divide warm potato salad evenly among them. Top each salad with a disc of goat cheese, and a sprinkle of scallions. Serve remaining dressing on the side.