1. Preheat the oven to 400 degrees F. Line a baking sheet with parchment. Spread the sweet potato cubes on the sheet, sprinkle with the cumin, smoked paprika, chili powder, and salt, and toss with a splash of water to coat. Roast for 20 to 25 minutes, stirring once, until tender and lightly caramelized.

2. While the sweet potatoes roast, make the sauce. Whisk all sauce ingredients together in a saucepan and bring to a gentle simmer over medium heat. Cook 5 to 7 minutes to thicken slightly. Taste and adjust salt.

3. In a large skillet, saute the onion over medium heat with 2 tablespoons of water until softened, about 4 minutes, adding water as needed. Add the garlic and cook 30 seconds, then add the black beans and spinach. Stir until the spinach wilts, about 2 minutes. Fold in the roasted sweet potatoes.

4. Assemble. Pour half a cup of sauce into the bottom of a 9 by 13 baking dish and tilt to coat. Warm the tortillas briefly (10 seconds in the microwave or a dry skillet) so they don't crack. Spoon about a third of a cup of filling down the center of each tortilla, roll tightly, and place seam-side down in the dish. Pour the remaining sauce over the top, covering every tortilla end-to-end.

5. Cover with foil and bake 20 minutes. Uncover and bake 5 more minutes until bubbling. Let rest 5 minutes, then scatter with cilantro and serve with avocado slices and lime.