These are a favorite of my friend Judy Micklewright’s six-year-old daughter, Becky, who could not stop eating them the first time I served them to her. The potato wedges make it easier to keep the stuffing in the tacos.
1. Cut the sweet potato lengthwise into 1/2 to 3/4-inch thick sticks.
2. Place a steamer basket in a sauté pan, and add 1 to 2 inches of water to the pan. Cover and bring to a simmer. Place the sweet potato wedges in the steamer, cover, and steam until the sweet potato is cooked through but not too soft, 7 to 10 minutes, making sure not to overcook. Remove the sweet potato from the pot and set aside.
3. In a large skillet, place the onion, garlic, and 2 tablespoons water. Cover and cook over low heat until the onion is translucent, about 10 minutes.
4. Add the reserved sweet potato, beans, corn, cumin, ancho chile, and salt to taste. Gently fold to coat the sweet potato with the spices. Cook over medium-low heat until heated through, 5 to 7 minutes. Remove from the heat.
5. Line a plate with a damp large, clean dish towel. Warm the tortillas one at a time for about 20 seconds on each side in a dry skillet set over medium heat. Or, if you have a gas stove, place a tortilla straight over the flame for a few seconds on each side. As you heat the tortillas, stack them on the damp towel and cover the tops of them with the towel to retain moisture.
6. Place the avocado in a small bowl and use a fork to gently mash it.
7. To form the taco, spread some avocado on half of each tortilla. Spoon some beans and sweet potato on top, and then add the tomato, scallions, and cilantro. Drizzle with some lime juice. Fold each tortilla in half. Serve at once.