Heat oven to 400°F. Pierce sweet potatoes several times with fork; place on large cookie sheet. Bake 1 hour or until tender. Let stand 10 minutes.
Meanwhile, in 12-inch skillet, heat oil over medium-high heat. Cook chicken, beans, corn and tomatoes in oil 5 minutes, stirring occasionally, until liquid is evaporated. Remove from heat. Stir in 2 tablespoons of the cilantro.
Cut sweet potatoes in half lengthwise, cutting almost to but not through bottom of potato; fluff pulp with fork. Return potatoes to cookie sheet. Top potatoes with chicken mixture. Sprinkle with cheese.
Bake about 5 minutes or until cheese is melted. Sprinkle with remaining 2 tablespoons cilantro. Top with sour cream.