Cut sweet potatoes into approximately 1-inch cubes. Heat olive oil in a large pan over medium heat. Add potatoes, cumin, coriander, and salt and saute for 15 minutes or until tender. Set aside to cool.When potatoes have cooled, add corn, black beans, scallions, and cilantro. In a separate bowl, combine chipotles, garlic, chili sauce, lime juice, and oil. Toss dressing with potato mixture, and serve.