Preheat the oven to 400°F. Toss the cubed sweet potatoes with the olive oil, salt, and pepper on a baking sheet. Roast for 20 minutes until tender.
While the potatoes roast, heat a skillet over medium heat. Add the diced onion and cook for 5 minutes until softened. Stir in the garlic and cumin and cook for 1 minute more.
In a large bowl, combine the roasted sweet potatoes, onion mixture, and black beans. Mix gently and season with additional salt and pepper if needed.
Spread 1/2 cup of enchilada sauce in the bottom of a 9x13 baking dish. Warm the tortillas briefly so they are flexible.
Spoon the filling into each tortilla, roll them up, and place them seam-side down in the baking dish. Pour the remaining cup of enchilada sauce over the top and sprinkle with the cheddar cheese.
Bake for 20 minutes until the cheese is melted and the edges are lightly browned. Let the dish rest for 5 minutes before serving.