Combine sweet potato and water in a large skillet; bring to a boil over high and cook, stirring occasionally, until sweet potato is mostly tender and water is completely evaporated, about 3 minutes.
Reduce heat to medium-high and add oil and onion; cook, stirring often, until onion is softened, about 3 more minutes. Add garlic, cumin, coriander, chili powder and oregano; cook, stirring constantly, until fragrant, about 1 minute. Add beans, tomatoes, broth, corn, quinoa and salt, and stir to combine. Bring to a boil. Reduce heat to medium; cover and cook until quinoa is tender and liquid has been completely absorbed, about 20 minutes. Remove from heat; uncover and top with cilantro and sour cream.
