Preheat oven to 350 degrees.
Peel the sweet potato, then cut it into 1/2 inch pieces.
Place the sweet potato on a baking sheet, drizzle olive oil and sprinkle with salt, pepper, chili powder, cumin powder and toss to coat the sweet potatoes in the oil and spices.
Roast the sweet potatoes for 20 minutes until soft and slightly browned, turning the sweet potatoes once halfway through. If you prefer to cook the sweet potatoes in the skillet, that is fine as well, you'll need to stir often to cook evenly.
While the sweet potatoes are roasting, chop an onion and saute in a pan until soft.
Add the drained and rinsed black beans, cumin, chili powder, and mix until well combined.
Stir in the roasted sweet potatoes and chopped spinach and stir to combine. Cook just until the spinach is wilted.
In a baking dish, pour a tablespoon or so of the enchilada sauce, then fill the corn tortillas with 2 tablespoons of the black bean and sweet potato mixture.
Roll the tortillas and place in the baking dish, rolled side down. Repeat until the baking dish is filled.
Top with shredded cheese and the remaining enchilada sauce. Cover and bake for 20 minutes until the cheese is melted and the tortillas are soft.