Preheat oven to 400 degrees. Peel and chop potatoes into bite- sized pieces and top with olive oil, cumin, and chili powder. Roast for 10 minutes, then turn heat up to 425 degrees and continue to roast for 15-20 more minutes or until golden brown.
Remove potatoes from onion, season with salt and pepper, and let cool.
Meanwhile, pulse all ingredients from the avocado down in a food processor to make dressing.
Top 1⁄4 of lettuce with a sprinkle or corn, black beans, sweet potato pieces, and a drizzle of the avocado dressing.