Heat oven to 425F. Toss sweet potato cubes with 1 tablespoon olive oil, cumin, smoked paprika, and 1/2 teaspoon salt on a large baking sheet. Spread in a single layer and roast for 20-25 minutes until tender and caramelized at the edges, stirring once halfway through. Let cool slightly.

While potatoes roast, heat a dry medium saucepan over medium heat. Toast the dried chiles for 30 seconds per side until fragrant but not blackened. Add 1 cup water, bring to a simmer, then remove from heat and let soak for 10 minutes. Transfer chiles and soaking liquid to a blender and puree until smooth. (If using chile powder, skip this step and blend 1/4 cup water with the powder.)

Heat remaining 1 tablespoon olive oil in the same saucepan over medium heat. Add garlic and cook for 30 seconds until fragrant. Stir in tomato paste and cook for 1 minute. Add the chile puree, vegetable broth, oregano, and remaining 1/4 teaspoon salt. Simmer for 8-10 minutes until slightly thickened. Taste and adjust salt.

Reduce oven to 375F. In a large bowl, combine roasted sweet potatoes, black beans, and 1/2 cup of the enchilada sauce. Stir gently to combine without mashing the potatoes completely.

Spread 1/2 cup sauce in the bottom of a 9x13 inch baking dish. Warm tortillas briefly in the microwave or on a dry skillet to make them pliable. Working with one at a time, spoon about 1/2 cup filling down the center of each tortilla, roll tightly, and place seam-side down in the baking dish. Fit all 8 snugly in a single layer.

Pour remaining sauce evenly over the enchiladas, making sure edges are covered so they don't dry out. Sprinkle with cheese. Bake uncovered for 20-25 minutes until bubbling and cheese is melted and spotty golden. Let rest for 5 minutes before serving. Top with cilantro and serve with lime wedges.