Preheat oven to 375°F. Oil a 9x13 baking dish.
Roast sweet potatoes with olive oil, salt, and pepper for 20 minutes until tender.
Sauté onion with cumin until soft, about 4 minutes.
Mix roasted sweet potato, black beans, and half the cheese. Stir gently.
Spoon filling into each tortilla, roll, and place seam-side down in dish.
Pour enchilada sauce over rolls and sprinkle remaining cheese on top.
Bake 15 minutes until cheese melts and edges bubble.
Garnish with cilantro if you like; serve with a simple salad.