Preheat oven to 375°F (190°C). Lightly oil a 9x13-inch baking dish.
Heat oil in a skillet over medium. Sauté onion 5 minutes until soft, add garlic 1 minute.
Add sweet potato, cumin, chili powder, and salt. Cook 8–10 minutes until tender.
Stir in black beans and heat through. Mash slightly with a fork for easier rolling.
Spoon 2–3 tbsp filling into each tortilla, roll, and place seam-side down in the dish.
Pour enchilada sauce over rolls and sprinkle with cheese.
Bake 20–25 minutes until bubbly and cheese melts. Cool, then freeze in portions or refrigerate to eat within 3 days.