Step 1: Preheat your oven to 400°F (200°C). Toss the cubed sweet potatoes with olive oil, cumin, and chili powder on a baking sheet. Roast for 20-25 minutes until tender.
Step 2: While potatoes roast, sauté the onion, bell pepper, and garlic in a pan over medium heat until softened. Stir in the black beans and remove from heat.
Step 3: Reduce oven temperature to 375°F (190°C). Spread a small amount of enchilada sauce on the bottom of a 9x13 inch baking dish.
Step 4: Create the first layer of the sweet potato and black bean enchilada casserole by placing tortillas over the sauce, cutting them to fit if necessary.
Step 5: Spread half of the roasted sweet potatoes and half of the black bean mixture over the tortillas. Top with more sauce and a layer of cheese.
Step 6: Repeat the layers of tortillas, remaining filling, sauce, and cheese until the sweet potato and black bean enchilada casserole is fully assembled.
Step 7: Cover with foil and bake for 20 minutes. Remove foil and bake for another 10-15 minutes until the cheese is bubbly and golden. Let rest for 10 minutes before slicing.