Prick sweet potatoes with a fork in several places. Microwave on high until tender all the way to the centre, 12 to 15 minutes.
Meanwhile, in a medium microwaveable bowl, combine beans, tomatoes, oil, cumin, coriander and salt; microwave on high until just heated through, 2 to 3 minutes.
When just cool enough to handle, slash each sweet potato lengthwise, press open to make a well in the centre and spoon the bean mixture into the well. Top each with a dollop of sour cream and a sprinkle of cilantro.