How to Make It
Heat oven to 450° F. In a blender, puree the tomatoes, chili powder, half the onion, 1 tablespoon of the oil, ½ teaspoon salt, and ¼ teaspoon pepper until smooth.
Heat 1 tablespoon of the remaining oil in a large skillet over medium-high heat. Add the remaining onion and half the garlic and cook until softened, 2 to 3 minutes. Add the black beans, sweet potato, oregano, and ¼ teaspoon each salt and pepper. Cook, tossing frequently, until the sweet potatoes are tender, 4 to 6 minutes. Transfer to a large bowl and let cool. Stir in 1 cup of the Cheddar.
Spread 1 cup of the tomato mixture in the bottom of a 9-by-13-inch baking dish. Roll up the bean mixture in the tortillas (about ½ cup each) and place the rolls seam-side down in the dish. Top with the remaining tomato sauce and 1 cup of Cheddar. Bake on the top rack of oven until the Cheddar is brown and bubbly, 10 to 15 minutes.
Meanwhile, wipe out the skillet and heat the remaining tablespoon of oil over medium-high heat. Add the remaining garlic and the scallion whites and cook, stirring, until fragrant, about 1 minute. Add the corn and ¼ teaspoon each salt and pepper. Cook, tossing frequently, until tender, 3 to 5 minutes more. Sprinkle the enchiladas with the scallion greens and serve with the corn.