Preheat the oven to 425 degrees.
Cut each sweet potato lengthwise into 8 wedges; halve long wedges crosswise.
On a large rimmed baking sheet lined with parchment paper, toss sweetpotatoes with oil, chili powder, 1 teaspoon coarse salt, and 1/4 teaspoon ground pepper, until coated. Arrange wedges, cut sides down. Roast potatoes until browned and tender, 15 to 20 minutes. Season with additional salt if needed.
Lay the wedges on a baking sheet and pile them high with cheese, beans and corn. Transfer the baking dish back into the oven and bake for a few minutes until the cheese is melted.
Remove the baking sheet from the oven and top the sweetpotatoes with the, scallions, cilantro, guacamole, salsa and sour cream.