Preheat the oven to 425 degrees . In a large saucepan, heat 2 tbsp. oil over medium. Add the onion, garlic, cumin, brown sugar, chipotle and adobo sauce. Season with salt and pepper and cook, stirring occasionally, until the onion softens, about 5 minutes. Add the beans, sweet potatoes and 2 cups water; bring to a boil. Cover, reduce the heat to low and simmer until the sweet potatoes are tender and liquid is absorbed, about 5 minutes.
In the bottom of a 9-by-13-inch baking dish, spread 1 1/3 cups enchilada sauce. Dredge both sides of the tortillas in the sauce. Divide the filling among the tortillas, roll up and arrange in the dish, seam side down. Top with the remaining sauce and cheese.
Bake the enchiladas until warmed through, about 10 minutes, then broil until the top is golden brown, 2 to 3 minutes. Let stand 15 minutes before serving.