Heat the oven to 220 C / 425 F with a rack in the middle. On a 33 x 46 cm / 13 x 18 inch sheet pan lined with parchment, toss the sweet potato cubes and diced onion with 1 tbsp olive oil, 1 tsp smoked paprika, 1/2 tsp cumin, and 1/2 tsp salt. Spread in a single layer and roast for 22 minutes, stirring once at 12 minutes, until the edges are browned and a fork slides in easily.

While the vegetables roast, heat 1 tbsp olive oil in a 3-quart / 2.8 L saucepan over medium heat. Cook the garlic for 30 seconds until fragrant, then stir in the chili powder, 1 tsp cumin, and 1 tsp smoked paprika for 20 seconds. Add the tomato sauce, broth, chopped chipotle, adobo sauce, and 1/4 tsp salt. Simmer for 12 minutes, stirring now and then, until it coats the back of a spoon.

Remove the sweet potatoes and lower the oven to 190 C / 375 F. In a large mixing bowl, combine the roasted vegetables, black beans, 60 g of the cheese, lime juice, and 2 tbsp cilantro. Press with a fork to mash about a quarter of the beans and a few potato cubes so the filling holds together but stays chunky.

Spread 120 ml / 1/2 cup of the sauce over the bottom of a 23 x 33 cm / 9 x 13 inch baking dish. Wrap the tortillas in a damp kitchen towel and microwave for 45 seconds until they bend without cracking. Spoon about 1/3 cup (90 g) filling down the center of each tortilla, roll snugly, and set seam side down in the dish, packing all 8 side by side.

Pour the remaining sauce over the enchiladas, covering the tortilla ends, and sprinkle with the remaining 60 g cheese. Cover with foil and bake for 12 minutes. Uncover and bake 8 minutes more, until the sauce bubbles at the edges and the cheese is melted with browned spots.

Rest the dish for 5 minutes. Top with sliced avocado and 2 tbsp cilantro, and serve with lime wedges.